Mr Justice Ribeiro PJ: 1. I agree with the judgment of Mr Justice Bokhary NPJ. Mr Justice Tang PJ: 2. I agree with the judgment of Mr Justice Bokhary NPJ. Mr Justice Fok PJ: 3. I agree with the judgment of Mr Justice Bokhary NPJ. Mr Justice Bokhary NPJ: Inferential reasoning 4. This appeal concerns how jurors are to be directed on inferential reasoning. Such directions might be couched in terms of the proper approach to circumstantial evidence, in terms of the proper approach to the drawing of inferences or even in terms of both. Inferential reasoning forms a very important part of the criminal justice system. It is by no means uncommon for the resolution of the crucial issue in a criminal case to depend on inferential reasoning upon facts proved or admitted. As good an example as any of such a case is one in which the crucial issue is whether a person who arrived in Hong Kong with dangerous drugs concealed in her or his luggage was aware of the presence of those dangerous drugs, and there is no admission by her or him of such knowledge. The present case is such a case. To borrow a phrase which Mr Baron Alderson is reported in Hodge’s Case (1838) 2 Lewin 227 at p 228 to have used when directing the jury, the prosecution’s case against the appellant is “made up of circumstances entirely”. Complaint 5. At her retrial before Mrs Justice Barnes and a jury, the appellant was convicted of unlawful trafficking in dangerous drugs consisting of 3.142 kilos of methamphetamine hydrochloride worth HK$2.3 million found concealed in the false-bottom of her suitcase, and was sentenced to 24 years’ imprisonment. That conviction was affirmed by the Court of Appeal (Mr Justice Lunn VP, Mr Justice McWalters JA and Mr Justice Pang). By leave of the Appeal Committee (Chief Justice Ma, Mr Justice Tang PJ and Mr Justice Fok PJ), the appellant now appeals to this Court upon a complaint that there has been to her disadvantage a departure from accepted norms which departure is so serious as to constitute a substantial and grave injustice. That complaint arises as follows. 6. There was evidence as to how the appellant did and did not react when confronted at the airport by customs officers with her suitcase in which the dangerous drugs were concealed. The crucial issue at the trial was whether the only reasonable inference was that the appellant knew that dangerous drugs were concealed in the suitcase. 7. Prosecuting counsel urged the jury to take the view that the appellant’s reaction and non-reaction pointed to her being aware of the presence of dangerous drugs in the suitcase. In her out-of-court statements, the appellant said that she was unaware of the presence of dangerous drugs in the suitcase, she having been duped into believing that what were concealed in the suitcase which she was given to carry were United States dollars which were being smuggled. Defence counsel, on the other hand, urged the jury to take the view that the appellant’s reaction and non-reaction were consistent with that belief. 8. In her summing-up, the judge dealt at considerable length with the evidence of the appellant’s reaction and non-reaction, but she made no specific reference to that evidence or the arguments thereon in the context of any of her directions on circumstantial evidence or the drawing of inferences. 9. That omission is what the appellant complains of as a departure from accepted norms giving rise to a substantial and grave injustice to her. Reaction and non-reaction of the appellant 10. Shortly stated, the details of the case were these. Early in the morning on 6 September 2010, the appellant, a middle-aged Vietnamese woman of good character and limited education, arrived in Hong Kong on a flight from Nairobi in Kenya. She having missed her connecting flight to Phnom Penh in Cambodia, an arrangement was made for her to travel there on another flight, being one departing later that morning. That arrangement involved retrieving her suitcase which had in Nairobi been checked-in to Phnom Penh. Having been retrieved, the suitcase was subjected to an x-ray examination. 11. That examination suggested that the suitcase had a false-bottom in which something was concealed. And the suitcase tested positive in an ionization test. The suitcase was emptied of its apparent contents consisting of clothing. Even then, as it seemed to a customs officer, the suitcase did not feel like an empty one. So the customs officers concerned decided to examine the suitcase in the appellant’s presence in the arrival hall. 12. The evidence of the appellant’s reaction and non-reaction when confronted with her suitcase containing the dangerous drugs concerned in this case consists of what the prosecution witnesses said then happened at the arrival hall. Their evidence was to this effect. With her suitcase in full view, the appellant was asked by Customs Officer Ma Hon-chuen in English “Is it your baggage?” All the persons present called as prosecution witnesses said that the appellant began to cry and squatted down next to the suitcase. One of them, an airline staff member, added that the appellant screamed “Wah!” Senior Customs Officer Ng Kwok-hong said that the appellant looked nervous and was shaking and trembling. Both Senior Customs Officer Ng and Customs Officer Ma said that the appellant unzipped the suitcase. Customs Officer Ma said that the appellant rummaged around in the suitcase before she was stopped from continuing to do so. At first, Senior Customs Officer Ng said, the appellant stood and watched as the contents of the suitcase were searched. But, he said, she sat down when the bottom of the suitcase was lifted out and the package containing the dangerous drugs was removed. At that stage, he said, she was expressionless. 13. Customs Officer Ma then performed a test with crystals to confirm the customs officers’ suspicion that the contents of the package were dangerous drugs. The appellant was then arrested and cautioned in both English and Chinese by Senior Customs Officer Ng. He said that she did not appear to understand and made no response. 14. Early in the afternoon on the same day, Senior Customs Officer Ng made a post-record of the arrest and cautioning of the appellant. With the aid of a Vietnamese interpreter, he asked her if she had anything to add. She said “The name tag on the black suitcase is mine. But the articles inside are not mine”. Exculpatory out-of-court statements which she relied upon 15. The appellant participated in an interview which began in the evening of 6 September and continued into the early morning of 7 September 2010. As to what the appellant said during that interview, there are three passages in the transcript of the interview which should be quoted. Of these, the first is the passage which reads: “The suitcase is mine. The South African asked me to take it to Cambodia. I did not know the South African.” 16. The second is the passage which reads: “In the hotel, I put a pair of black jeans and one set of red top and trousers into the suitcase. I saw that there were tops, trousers, shoes and slippers inside the suitcase. I knew nothing else. I closed the suitcase and a zipper without taking a look at its contents.” 17. And the third is the passage which reads: “I do not know what the dangerous drug methamphetamine is. At 18 ‘Square’, Vietnam, my younger sister opened a coffee shop. I saw a person called Mai-Ka in the coffee shop. He/she asked me to take US dollar from South Africa to Cambodia. He/she will give me US$ 1,500 upon arrival. As I have liver disease, I need the money for treatment.” 18. The appellant went on to say at the interview that she understood that United States dollars were inside the suitcase but that she had not checked to see if that was so. 19. At 1:35 am on 7 September 2010, the appellant, having been formally charged with unlawfully trafficking in the dangerous drugs found in her suitcase, made this answer to the charge: “I did not know there were dangerous drugs in the suitcase. I was deceived by others. I know I was wrong. I hope the judge will pass a lenient sentence so that I can go home soon as possible.” 20. It having been mentioned that the trial at which Mrs Justice Barnes presided was a retrial, a word should, for the sake of completeness, be said about the first trial. That trial was before Mr Justice Line and a jury. It resulted in the appellant being convicted and sentenced to a term of 26 years’ imprisonment (being two years longer than the term which Mrs Justice Barnes later imposed at the retrial). The appellant’s conviction at that trial was quashed by the Court of Appeal (Mr Justice Stock VP and Mr Justice Cheung JA, Mr Justice Wright dissenting) on a ground which does not arise in the present appeal. A retrial was ordered by that division of the Court of Appeal. And the appellant was then retried before Mrs Justice Barnes and a jury. 21. At the retrial, the appellant did not testify. She relied on her exculpatory out-of-court statements. These were dealt with extensively by her counsel in his final speech to the jury. The defence called one witness, a Vietnamese woman who had at one time been an inmate in the same prison as the appellant was in. This witness spoke of the appellant as a kind person, and produced a letter written to her by the appellant. The grammatical mistakes in that letter, Mr Justice Lunn VP said, spoke to the appellant’s limited level of literacy. Special direction on the drawing of inferences 22. Before continuing with the facts of the present case, a word should be said on the relevant law as stated by this Court in Tang Kwok Wah v HKSAR (2002) 5 HKCFAR 209, which is this. It is normally unnecessary to give the jury any special direction on how they are to approach circumstantial evidence. Whether the prosecution’s case depends wholly or in part on circumstantial evidence, it is normally sufficient that the jury be directed that they may not convict unless they are sure of guilt. There may, however, be exceptional circumstances in which it may be desirable or even necessary to give the jury a special direction on the drawing of inferences by telling them that no inference is to be drawn against the accused unless it is the only reasonable inference. Was given, but was it given adequately? 23. Mrs Justice Barnes rightly took the view that the circumstances of the present case called for a special direction. And she gave the jury such a direction. Was it an adequate one in the circumstances? Summing-up should relate the law that the jurors have to apply to the context in which they have to apply it 24. In the course of a summing-up, jurors receive many directions on the law. They must be assisted to see those directions in the context of the evidence and the arguments thereon. Where inferential reasoning is involved, the summing-up is likely to contain repeated directions on the approach to inferential reasoning. It is to be expected that at least once in the course of the summing-up, the directions on inferential reasoning would be specifically set in the context of the evidence and the arguments thereon. A summing-up should relate the law that the jurors have to apply to the context in which they have to apply it. How that is to be done in regard to inferential reasoning is addressed in the specimen direction on the drawing of inferences to be found at p 21.3 of the Specimen Directions in Jury Trials issued by the Judicial Institute in September 2013. 25. That specimen direction, after indicating that no inference is to be drawn against the accused unless it is the only reasonable one, immediately continues as follows: “[In this particular case, the prosecution says that there is direct evidence that (specify one or a number of primary facts which the prosecution say are clearly shown) and the prosecution says that the only reasonable inference to draw from those facts is that …. On the other hand the defence says that although that might be one inference which could be drawn, it is not the only reasonable inference to draw; and that another inference one might reasonably draw is that ….]” (Italics in the original.) 26. Relevant to that, what counsel said in their final speeches about the appellant’s reaction and non-reaction and the conclusion to be drawn from the same is as follows. Prosecuting counsel’s arguments in final speech: the appellant was a knowing drug courier 27. Prosecuting counsel said this to the jury: “And one other reason why I suggest to you that you are sure she committed this offence, and this, I suggest, is overwhelming. When she’s brought through the red channel, she goes, ‘Ahhh’ and she starts to sob or cry, doesn’t she? That’s the evidence, when the suitcase is pointed to her. And then she immediately opens it up, so she clearly knows it’s not locked, and she rummages around. Now, if those aren’t hers, why is she rummaging around? If they are hers, there’s no purse in there, there’s no documents in there, there’s no underwear in there, right? Why is she rummaging around immediately? She’s rummaging around because she wants to see if the drugs have come out of the bottom of the suitcase. She wants to see if they’re already discovered. And that’s not my overwhelming point. I’ve got a better one. She stopped. She’s been crying. She’s not crying and sobbing throughout. She’s obviously very nervous, and so would you be in her shoes, we’ve got to accept that. We’d all be terrified; innocent or guilty, we’d all be terrified in her shoes. But when it comes to the stage at which the suitcase is taken apart, if you are innocent, what’s the stage that you would go again, ‘Ahhh’? She’s done it once. It’s a natural reaction. You might think everybody would notice if all of a sudden, the bottom of your suitcase is peeled open and there was a bulky package. Not a flat, linear package that you might pack money in, but a bulky package that you saw. And even if she was a cool cucumber, even if she was very cool and calm and didn’t react to that, at the stage that somebody sticks a knife into the package and pulls out a crystal and sticks it into some fluid that turns blue, where was her reaction to that? And it is that, ladies and gentlemen, that convicts this woman. You can be sure that her lack of response to that is indicative of the fact she knew what was inside her suitcase was drugs, it wasn’t money, it was drugs.” Defence counsel’s arguments in final speech: the appellant had been duped into believing that she was smuggling money 28. At an early stage of his final speech, defence counsel stated the defence’s case that, as far as the appellant knew, she was acting as a smuggler of money and not as a drug courier. He observed that “[i]f it was Hong Kong, she could bring money in and out as she wished but, presumably, the position is different in other countries”. Turning to the appellant’s reaction and non-reaction, he said: “You may recall that when she was first taxed with just the simple question, ‘Is this your bag?’, she let out a call and squatted down, unzipped it with the intention of going into the bag. Is that the act of a drug trafficker that’s trafficking in $2 million worth of drugs? It looked like she was apparently trying to proffer up something to them, like the money, for example. It’s not the kind of act you’d expect from a cool and calm drug trafficker. Later on – you heard that she was sobbing, crying – and then later on, before she’s actually cautioned and arrested, one of the officers uses the ‘narco test’, do you remember, he put some chemicals on the powder and they turned blue. No reaction. She cries, squats down and looks in the bag when they simply ask her is it her bag. Later on, when, to the officer’s point of view, something really serious had happened, they’d found a positive test for drugs, she has no reaction. She simply doesn’t know what’s going on. If she’d cried like she did before when she was simply asked the question ‘Is this your bag?’, wouldn’t we have expected her to have gone berserk when the drugs turned the wrong colour and gave off a reaction to show that these really were dangerous drugs? But no, she just simply stands there. She has no idea what that substance is. I’d suggest, ladies and gentlemen.” 29. So, on the crucial issue of knowledge, the rival stances as to the inference to be drawn from the appellant’s reaction and non-reaction were in effect these. Prosecuting counsel argued that the only reasonable inference to be drawn from the appellant’s reaction and non-reaction, particularly her non-reaction, was that she knew that dangerous drugs were concealed in the suitcase. Defence counsel argued that the appellant’s reaction and non-reaction were more consistent with, or at least reasonably consistent with, a belief on her part that United States dollars were concealed in her suitcase. McGill’s case is different from the present case 30. Both in the Court of Appeal and here, the respondent cited the decision of the High Court of Justiciary in McGill v Her Majesty’s Advocate 2000 SCCR 253. McGill had recently bought a car. While he was driving that car with a passenger in it, the police stopped it. The police found drugs hidden behind the glove compartment at the passenger side of the car. McGill was charged with being concerned in the supply of those drugs. The prosecution adduced evidence that his reaction was one of shock when the police stopped the car and started to search it but that he showed no surprise when the drugs were found. 31. A submission of no case to answer was made on McGill’s behalf. It was rejected. So the case went to the jury. They convicted McGill. He appealed against his conviction on the ground that there was insufficient evidence to show that he had knowledge of the presence of the drugs found in his car and that the judge had erred in rejecting the submission of no case to answer. McGill’s appeal failed. Delivering the opinion of the court, Lord Prosser said that taken along with the other evidence, McGill’s reaction to the stopping of the car and the start of the search of it and his non-reaction to the finding of the drugs justified the judge’s rejection of the submission of no case to answer. 32. McGill’s case concerns whether there was a case to go to the jury. It does not concern the sufficiency or otherwise of the directions which the jury received, which is what the present case concerns. 33. Therein lies the distinction in law between McGill’s case and the present case. There is also a distinction between them on the facts, which is this. There was no suggestion of McGill being in fear of something other than drugs being found in his car. On the other hand, the appellant’s out-of-court statements were to the effect that there was something other than drugs that she feared had been, or would be, discovered in her suitcase, namely smuggled United States dollars. That does not render her reaction and non-reaction irrelevant. It does, however, add to the importance of the directions to the jury on the proper approach to inferential reasoning being specifically set in the context of the evidence and the arguments thereon. So is White’s case 34. The respondent also cited the decision of the Supreme Court of Canada in R v White 2011 SCC 13. That was a murder case in which the evidence relied upon against White included evidence that he had fled the scene after shooting the victim. The respondent cited it for the proposition that evidence of post-offence conduct does not give rise to any special rule of admissibility or to any need for a special warning. But the present case raises no question as to the admissibility of post-offence conduct. Nor does it raise any question of a special warning to be given in respect of post-offence conduct as such. 35. There are various types of post-offence conduct that the prosecution may seek to rely upon in any given case. Reaction and non-reaction (as in McGill’s case and the present case) is one type. Other types include, for example, flight (as in White’s case) and lies. There are particular directions which jurors are to be given on flight, and there are particular directions which jurors are to be given on lies. 36. The present case involves the directions that jurors are to be given on inferential reasoning. It so happens that the facts from which the jury were asked to infer guilty knowledge in the present case consist of post-offence conduct. But the essential requirements of directions on inferential reasoning are the same whether the facts from which jurors are asked to draw an inference against the accused consist of post-offence conduct or consist of something other than such conduct. Zen’s case does not undermine the specimen direction 37. Another decision to which the respondent has drawn attention is that of the Court of Appeal in HKSAR v Zen Xiulan [2016]4 HKLRD 237. That was a drug-trafficking case in which the prosecution alleged, while Ms Zen denied, that she was aware of the dangerous drugs concealed in the lining of the handbag which she was carrying upon arrival in Hong Kong on a flight from Kuala Lumpur in Malaysia. What the Court of Appeal really held in that case is no more than this. The judge in that case had dealt with all the evidence on the basis of which an inference of knowledge could be drawn against the accused. And there was no need in the circumstances of that case for the judge to tell the jury what evidence they could and could not rely on for the purpose of drawing that inference. That could in the circumstances of that case be left to their common sense. 38. Quite simply, the decision in Zen’s case does not undermine, nor does it even seek to undermine, the specimen direction on the drawing of inferences issued by the Judicial Institute. Crown Court Bench Book 39. Lest it be thought that that specimen direction issued by the Judicial Institute stands alone, mention should be made of what the Crown Court Bench Book issued in March 2010 by the Judicial Studies Board in England and Wales says about the directions to give a jury on circumstantial evidence and the drawing of inferences. The Court is indebted to one of its Judicial Assistants, Mr Benjamin Lam, for drawing its attention to that publication. It is there said (at p 36) that directions on circumstantial evidence and the drawing of inferences should include “a summary of the defence case as to the disputed evidence, the identification of evidence which may rebut the inference of guilt, and the disputed inferences”. The specimen which is then provided (at p 37) is of a direction on inferential reasoning in the course of which and as a part of which the judge specifically draws the jury’s attention to: the evidence on which the prosecution places particular reliance; why the prosecution places particular reliance on that evidence; and what the defence case is. That specimen direction on inferential reasoning bears out the appellant’s point at least as clearly as, and perhaps even more clearly than, the Judicial Institute’s specimen direction on such reasoning. Why did the Court of Appeal decide against the appellant? 40. Coming back to the present case, this is what the Court of Appeal said (in para 38 of their judgment) after dealing with what each counsel said in final speech and with what the judge said and did not say when summing up: “Given that the judge had dealt with [the evidence of the appellant’s reaction and non-reaction] at considerable length and that it has been the subject of competing submissions and the respective closing speeches of counsel, the absence of a specific reference to that evidence in the context of directions as to the drawing of inferences is surprising. With respect to the judge, specific reference ought to have been made by her to the evidence of [the appellant’s] reactions and non-reaction from the time that she was confronted with the suitcase. That ought to have been done as part of the general direction given in respect of the circumstantial evidence and the drawing of inferences.” 41. On what basis did the Court of Appeal decide against the appellant despite that omission? Jurors look to the judge for the law 42. As to that, one of the things to which the Court of Appeal attached weight is that, as they put it, “the judge directed the jury that they should take into account the speeches of counsel”. 43. No reference to prosecuting counsel’s speech could begin to cure, or contribute to the curing of, the disadvantage to the appellant resulting from the omission. 44. As for reference to defence counsel’s speech, that speech was not calculated to provide that which the judge eventually omitted to provide. And even if it was so calculated, it would not have been enough. Delivering the advice of the Privy Council in Lawrence v R [1933] AC 699, an appeal against conviction which succeeded on the “substantial and grave injustice” ground, Lord Atkin famously observed (at p 707) that “[j]urors are apt to be suspicious of law as propounded by the defence; they look to the judge for authoritative statement of it”. That was said in the context of a judge’s failure to direct the jury on the onus of proof. But the same thing can be said in the present context. The point goes to the respective roles of the judge and of the jury. What jurors infer is a matter of fact for them, but the proper approach to inferential reasoning is something which they are to take from the judge as a matter of law. 45. There can be situations in which a judge’s reference to counsel’s speeches will cure, or contribute to curing, a summing-up that would otherwise have been unacceptable. But the present situation is not such a situation. 46. Ultimately, the basis on which the Court of Appeal decided against the appellant was, as they stated it (in para 42 of their judgment), this: “We are satisfied that the judge’s omission was not material. The jury was appropriately directed, in particular repeatedly so in respect of the burden and standard of proof and in respect of the drawing of inferences adverse to [the appellant]. There was no need to give a further special direction.” Special direction on drawing inferences should be specifically set in context 47. It is true that, as the Court of Appeal observed, the judge had appropriately directed the jury on the burden and standard of proof. There would have been another ground of appeal if the jury had not been appropriately directed on those matters. That there is no cause for complaint on those matters does not cure, or contribute to curing, the omission of which complaint is made. 48. The judge decided, and rightly, that a special direction on the drawing of inferences was called for in the circumstances of the present case. And the special direction which she gave was correct to the extent that it did give the jury to understand that no inference was to be drawn against the appellant unless it was the only reasonable one. But, surprisingly as the Court of Appeal unsurprisingly felt, the judge never gave the jury any inferential reasoning direction specifically set in the context of the evidence and the arguments thereon. 49. The omission cannot be regarded as immaterial. It was not an omission to give a “further” special direction but an omission to give a correct direction on inferential reasoning. So should a general direction on circumstantial evidence 50. Where the prosecution seeks to prove a fact by evidence of other facts, it may, depending on the circumstances, be appropriate to direct the jury on inferential reasoning by giving them a special direction on the drawing of inferences. Or it may, depending on the circumstances, be appropriate to direct the jury on inferential reasoning simply by giving them a general direction on the proper approach to circumstantial evidence. 51. It is not to be thought that those two ways of directing a jury on inferential reasoning are mutually exclusive or incompatible with the other. Nor is it to be thought that general directions on circumstantial evidence need not be set in the context of the evidence and the arguments thereon. 52. On those points, the case of R v Onufrejczyk [1955] 1 QB 388 is highly instructive. It was a case of a conviction for murder even though the victim’s body was never found. Lord Chief Justice Goddard, delivering the judgment of the Court of Criminal Appeal dismissing Onufrejczyk’s appeal, said (at p 394) that “the fact of death, like any other fact, can be proved by circumstantial evidence, that is to say, evidence of facts which lead to one conclusion, provided that the jury are satisfied and are warned that it must lead to one conclusion only”. 53. At Onufrejczyk’s trial, Mr Justice Oliver had (as one sees at p 395) weaved his references to the evidence and the arguments thereon into his directions to the jury on the approach to circumstantial evidence, using the expressions “no rational hypothesis except” and “no rational explanation…except”. Those expressions and the Lord Chief Justice’s expression “one conclusion only” convey the same message as the expression “only reasonable inference” and the expression “irresistible inference” which is sometimes used in its stead. 54. While speaking for the most part in terms of circumstantial evidence, the Lord Chief Justice also spoke (at pp 400-401) of what the jury could “infer”. 55. A summing-up might to some extent be influenced by the fact that counsel, when addressing the jury, happen to use an expression other than, albeit meaning the same thing as, the expression which the judge prefers. Suppose counsel used expressions such as “being satisfied beyond reasonable doubt”, but the judge prefers expressions such as “being sure”. Then the judge may see fit, while generally using expressions such as “being sure”, to tell the jury that being “satisfied beyond reasonable doubt” means the same thing as “being sure”. Another such example is the situation in which counsel talked about “circumstantial evidence” when addressing the jury, but the judge chooses to give the jury a special direction on the drawing of inferences. In such a situation, the judge may consider it appropriate to include some reference to the proper approach to circumstantial evidence, making it clear to the jury that there is no inconsistency between that approach and the rule that no inference is to be drawn against the accused unless it is the only reasonable inference. Jury directions must be tailored to the circumstances of the case 56. To be helpful to a jury, the directions to them must be tailored to the circumstances of the case. For the purposes of the task which jurors have to perform, the circumstances of a case consist of the evidence and the arguments thereon. In Plomp v R (1963) 110 CLR 234, a case decided by the High Court of Australia, Mr Justice Menzies spoke (at p 252) of the “customary direction where circumstantial evidence is relied upon to prove guilt, that to enable a jury to bring in a verdict of guilty it is necessary not only that it should be a rational inference but the only rational inference that the circumstances would enable them to draw”. It is always a matter of the circumstances. 57. Where inferential reasoning is concerned, by far the most helpful reference to the circumstances of the case would be one made in the course of, and as part of, the directions on such reasoning. Whatever the form or forms in which a judge sees fit to direct the jury on inferential reasoning, and however many times such directions are repeated in the course of the summing-up, it always remains important that there be at least one instance in which the directions on such reasoning are specifically set in the context of the evidence and the arguments thereon. Departure from accepted norms 58. The directions on inferential reasoning given in the present case do not include any direction specifically set in the context of the evidence of the appellant’s reaction and non-reaction and the rival arguments thereon. That omission constitutes a departure from the accepted norm that where directions on inferential reasoning are necessary, then whatever form or forms such directions take, and however many times they are repeated, there will be at least one instance in which the jurors are given directions on such reasoning that are specifically set in the context of the evidence and the arguments thereon. So serious as to constitute a substantial and grave injustice 59. In so far as the omission pertained to defence counsel’s arguments on the conclusion to be drawn from the appellant’s reaction and non-reaction, the departure from accepted norms was indisputably to the appellant’s disadvantage. The omission was, after all, in respect of the crucial issue in the case, being the issue on which guilt or innocence turned. Was the evidence of the appellant’s reaction and non-reaction consistent only with her being aware that dangerous drugs were concealed in her suitcase? Or was that evidence at least also consistent with a belief on her part that what were concealed in her suitcase were United States dollars? In other words, was an inference of guilty knowledge the only reasonable one to be drawn? 60. Prosecuting counsel had advanced her arguments against the appellant on that crucial issue in most emphatic terms. Having placed considerable reliance on the appellant’s reaction, prosecuting counsel went on to argue that the prosecution had an even better point based on the appellant’s non-reaction, saying to the jury: “And it is that, ladies and gentlemen, that convicts this woman.” The saying (attributed to the renowned prosecutor Sir Richard Muir) that “[t]he duty of a prosecutor is to prosecute” is often cited to make the point that, within the bounds of fairness of course, prosecuting counsel is entitled to put the prosecution’s case as forcefully as is warranted by the evidence. That is one side of the coin. The other side of the same coin is the duty of a defender to defend. 61. As was his duty, defence counsel advanced arguments in the appellant’s favour to meet the arguments advanced against her by prosecuting counsel. They were arguments in the appellant’s favour worthy of a correctly directed jury’s attention. 62. Naturally and properly, the judge had taken pains to accord the appellant a fair trial. Just as naturally and properly, the Court of Appeal reviewed the appellant’s conviction with their customary conscientiousness. A trial judge’s assessment on how jurors ought to be directed in any given case is not lightly to be disturbed. Nor is an intermediate appellate court’s view that the way in which jurors were directed in any given case is acceptable or at least not fatal. But in the particular circumstances of the present case, it was vital that there be a direction on inferential reasoning specifically set in the context of the evidence and the arguments thereon. The absence of any such direction in the present case is, therefore, fatal to the conviction. 63. For the foregoing reasons, there is no escaping the conclusion that this departure from accepted norms was not only to the appellant’s disadvantage but was, in the particular circumstances of the present case, so seriously to her disadvantage as to constitute a substantial and grave injustice to her. Conviction quashed 64. Accordingly, I would allow this appeal to quash the appellant’s conviction. Retrial ordered 65. The stance adopted by counsel for the respondent at the hearing of the appeal is that if the conviction were quashed, then a retrial should be ordered. On the question of whether we should order a retrial, counsel for the appellant invited us to bear in mind that the appellant, who has already been tried twice, has been in custody since 6 September 2010. Each case of course depends ultimately on its own circumstances. Nevertheless, it is worth mentioning that there have been occasions on which this Court has ordered retrials of persons who had been in custody for periods comparable to the one for which the appellant has now been in custody. Even after that period has been deducted, the appellant would still face a long term of imprisonment to serve if convicted at a retrial. There is simply no getting away from the fact that the offence alleged against the appellant has to be regarded as a very serious one indeed. Lest saying more might prejudice the appellant’s retrial, suffice it to conclude by saying that, all things considered, the appropriate course is to order that the appellant be retried. I would so order. Lord Walker of Gestingthorpe NPJ: 66. I agree with the judgment of Mr Justice Bokhary NPJ. Mr Justice Ribeiro PJ: 67. The Court unanimously allows the appeal to quash the conviction and order a retrial. Mr Cheng Huan SC and Mr Edward H M Tang, instructed by Tanner De Witt, assigned by the Director of Legal Aid, for the Appellant Mr David Leung SC, DDPP and Mr Ira Lui, SPP of the Department of Justice, for the Respondent