Trill The Trill ( or Trills ) were a humanoid species native to the planet . A small percentage of the Trill population co - existed with a sentient symbiotic organism known as a symbiont inside their bodies . The resulting joined Trills had personalities which were a synthesis of the two beings including the memories , and to some extent the personalities , of the previous hosts of the symbiont . This way , the joined being gained all the skills and occupations of the previous hosts . As late as 2367 , the fact that some Trills exist as a joined symbiotic species was widely unknown , even to Federation scientist s . ( ) Physiology . Most Trills are distinguished by two rows of spots going down each side of their bodies , from forehead to toe . Their skin color could vary . One of the main neurotransmitter s in the Trill brain is isoboramine . ( ) Joined Trills are also extremely allergic to insect bites ; the biochemical connections between the host and symbiont cannot tolerate the reaction caused by the insect ' s venom . ( ) It may be noted that Trill are known for having cold hands . ( ) The few Trills that are given a symbiont are typically joined in their early - to mid - twenties . The physical process of being joined is irreversible . Once joined , the host and symbiont are dependent on each other after ninety - three hours . If the symbiont is removed from the host , symbiont and host will die within hours , even if they are otherwise healthy , unless they are reimplanted with another host or symbiont . ( ) The brain of a joined Trill has two cerebral nuclei and two different brain wave patterns . Julian Bashir compared them with two linked computer s , which both work for the same task , in 2369 . ( ) Society . Despite the relatively unusual nature of being a joined species , that aspect of their culture was not widely known until 2367 , when the Odan symbiont had to be given a new host during the middle of tense negotiations on Peliar Zel . Such a public example of the dual nature of the Trill brought to the forefront what had previously been a very private matter to Trill for several millennia . ( ) In contrast to the greater revelation of their nature , the Trill are not a secretive species . To them , the joined nature of their culture is normal and not something they would think to comment on without prompting . Indeed , joined Trills can be seen as particularly genial and many have served the Federation as distinguished ambassadors , including Odan and Dax . Jadzia Dax joked that Trills don ' t look for romance the way Human s do . Joined Trills consider it quite a nuisance and view it as a weakness of the young . While hosts may have romantic feelings as often as any other sentient species , symbionts try to live on a higher , more spiritual plane and try to rise above those sorts of temptations . ( ) Trill law forbids reassociation between subsequent hosts of joined persons , whose symbionts were romantically involved in their previous hosts , and the people who the previous hosts were romantically involved with . This is because the main purpose of the transfer of symbionts is to experience new things in life . Trills who are found guilty of reassociation are expelled from Trill society , meaning that their symbionts die with their current host . ( ) Beyond the illegality of it , Trills almost universally view reassociation as a cultural taboo , but the degree to which they follow it is up to the individual . Some Trill take it so far as to not associate with any of their previous hosts ' friends , family and colleagues , beyond the rare chance encounter . Others have a very narrow interpretation , and freely associate with the friends and acquaintances of their previous hosts & symbionts , avoiding only those with whom their previous hosts were intimately involved . The Trill are a technologically advanced species and the Trill Science Ministry is a leading center of learning and experimentation . ( ) Joining . On average , only three hundred symbionts are available for hosting each year and about a thousand Trills apply for joining . Because there are many more humanoid Trills than symbionts , prospective hosts are weeded out by a demanding selection procedure , overseen by the Symbiosis Commission . ( ) The competition for the few symbionts is fierce and attracts the brightest and most highly motivated of Trill society . Often , the would - be hosts excel in their chosen fields and it is not uncommon for them to hold several degrees or distinctions prior to their joining . Prospective hosts may eventually become initiates under the supervision of a field docent , a joined Trill who evaluates the prospective host ' s suitability for joining and makes a recommendation to the Commission . A negative recommendation usually means the initiate is cut from the joining program . ( ) Common belief in Trill society holds that only one in a thousand Trills make acceptable hosts . In fact , this figure is vastly understated , and nearly half of the Trill population is capable of being joined . The myth is perpetuated very carefully , though , in order to avoid widespread chaos which would probably arise if the information were made public , since the symbionts would become , essentially , objects to be fought over , as people fought to gain the few prized symbionts . ( ) Unless the joined Trill objects , a prospective host may request a specific symbiont . If a host is weak , the personality of the symbiont will overwhelm it . Joined Trills have several tools at their disposal for dealing with various aspects of their previous hosts . The telepathic ceremony of " zhian ' tara " allows a current host to divest the symbiont of the personality and all the memories of a previous host , which are temporarily hosted in volunteers . The transferring process is performed and supervised by a symbiont , an unjoined Trill telepath . The ceremony creates a chance for closure by having the new host address the previous hosts directly , as a means of distinguishing their voices and cementing the sense of finality of its latest transition . Similarly , the Rite of Emergence can focus the voice of a single previous host among the memories of the other , allowing for a more direct conversation in times of need for the current host . The " zhian ' tara " ritual is roughly similar to the Vulcan " fal - tor - pan " ritual , since both enable the respective species to perform a synaptic pattern displacement , the transfer of what could be considered as a soul ( " katra " , " pagh " , etc . ) . ( ) Mirror universe . In the mirror universe , it was unclear which side ( if any ) the Trill government took in the conflict between the Klingon - Cardassian Alliance and the Terran Rebellion . A number of individual Trills were part of the Rebellion , while others would attempt to remain non - aligned . ( ) Appendices . Appearances . A list of all appearances of Trills ( excluding Jadzia and Ezri ' s DS9 appearances ) . Background information . Introduction . At the time the concept of Trills was first conceived , the idea was ( at least in the opinion of Brannon Braga ) " very fresh . " Ronald D . Moore suspected that many freelance writers would have centrally featured the Trill in the premise of , the first episode to depict a Trill , to a degree more than the installment actually does . ( " " , p . 221 ) For the make - up team tasked with designing the look of the Trills , the challenge was threefold : the humanoid host , the abdominal cavity and the symbiont . ( " " , p . 116 ) The facial appearance of Trills was originally designed by Michael Westmore for " The Host " . " " The original Trills had a forehead appliance and a little nosepiece , " " he said . ( " Cinefantastique " , Vol . 23 , No . 6 , p . 31 ) The appliance used for the nose and forehead downplayed the alien nature of the Trills , causing them to seem just slightly extraterrestrial but still overtly human . ( " " , pp . 116 - 117 ) The requirement of creating a body cavity for the symbiont was much more challenging . The make - up department crafted an appliance for the stomach area , covered with enough hair to blend in with the actor ' s own body , with three air - bladders beneath the fake skin . Activating the bladders , by blowing air into them via tubes , could give the impression that the skin was being moved by the symbiont living inside the host . Since the stomach appliance was made with extremely soft rubber , the pulsating bladders were able to swell inside the whole area of the cavity , expanding it noticeably , which made for a very effective shot . ( " " , p . 117 ) Becoming regulars . At first , Trills were not to have featured as much on as they ended up being , because the creative staff initially considered a variety of alien species for the character of Jadzia Dax . " " Of them , the Trill seemed the most interesting , " " noted Michael Piller . ( " Cinefantastique " , Vol . 23 , No . 6 , p . 20 ) He also said , " " Having a Trill seemed like a really , really good idea , at the time . " " ( " New Frontiers : The Story of " Deep Space Nine " " , DS9 Season 2 DVD special features ) Once that species was selected , explaining the concept of a Trill to those who auditioned for the role proved difficult , hampering the casting process . ( " Star Trek - Where No One Has Gone Before " , paperback ed . , p . 179 ) In the series bible of " Star Trek : Deep Space Nine " , the Trill symbionts and humanoids were said to have lived underground and on the surface of Trill respectively , " many centuries ago . " The description continued , " " Due to an environmental disaster , they were forced to ' join ' to survive . As time went on , this mutual support evolved into a biological interdependency and thus two individuals became one – they speak with one voice ( you can ' t ask to speak with the symbiont or the host , only the combined lifeform ) . " " It was initially planned for the Trills of DS9 to look basically identical to Odan , who had established the Trill appearance in " The Host " . The make - up was consequently to still consist of several distinguishing marks on the forehead . ( " Cinefantastique " , Vol . 23 , No . 6 , p . 21 ) Actress Terry Farrell recalled how the Trill makeup was being planned when she was cast as Jadzia Dax ; " " [ Makeup Supervisor Michael ] Westmore [ . . . ] was about to put this whole thing on me [ . . . ] I didn ' t know that the [ makeup ] testing would take months to figure out that I didn ' t need a forehead . " " ( " Crew Dossier : Jadzia Dax " , DS9 Season 2 DVD special features ) Indeed , a new prosthetic forehead , much like the original , was designed by Westmore . ( " Crew Dossier : Jadzia Dax " , DS9 Season 2 DVD special features ) The appliance was filmed in test footage involving Farrell . ( " " , p . 7 ; " Crew Dossier : Jadzia Dax " , DS9 Season 2 DVD special features ) At first , the forehead matching Odan ' s was used for only two days . " " Then they kept reducing it with each test , " " related Farrell , " " until it really looked like someone had just hit me in the forehead . But Paramount didn ' t want to make me look strange . " " ( " " , p . 7 ) The forehead appliance was used over the course of a few weeks . ( " Crew Dossier : Jadzia Dax " , DS9 Season 2 DVD special features ) " " We had only shot one of her scenes , which [ the producers ] wanted to redo for some other reason , so they took a new look at the makeup , " " explained Westmore . ( ) After Paramount executives watched the dailies of Terry Farrell in DS9 pilot , they issued a rare ultimatum about the Trill make - up scheme . The executives insisted the make - up be changed via removal of the forehead markings ; having spent a long time seeking a beautiful actress for the role of Dax , Paramount wanted to avoid Farrell being defaced by prosthetics . ( " Cinefantastique " , Vol . 23 , No . 6 , p . 21 ) The actress offered , " " I just remember that somebody said , ' What did you do to her ? She used to be beautiful and you gave her this weird head ! " " ( " Crew Dossier : Jadzia Dax " , DS9 Season 2 DVD special features ) The alarmed reaction to the Trill forehead finally resulted in the more common spots seen on " Deep Space Nine " . Hence , the reasons for the change were purely cosmetic . ( " " , p . 7 ; " Crew Dossier : Jadzia Dax " , DS9 Season 2 DVD special features ) Like the unused forehead , the Trill spots were designed by Michael Westmore . ( " Crew Dossier : Jadzia Dax " , DS9 Season 2 DVD special features ) He took inspiration for the spots from Kriosian make - up in . ( " TV Zone " , Special # 34 , p . 12 ) The DS9 makeup team thought the Trill spots would look sexier than the earlier ones , though . ( " Crew Dossier : Jadzia Dax " , DS9 Season 2 DVD special features ) " " I didn ' t want to do the exact same thing , " " recollected Westmore , " " so we experimented around the front of Terry ' s face and the powers - that - be finally accepted that design . " " ( " TV Zone " , Special # 34 , p . 12 ) The resultant distinguishing marks were tested over a couple of weeks . One of the tests , labeled " Take 3 " , was filmed with a TNG clapperboard . ( " Crew Dossier : Jadzia Dax " , DS9 Season 2 DVD special features ) Observing the entire make - up layout usually worn by Farrell , Westmore said , " " Aside from her regular beauty makeup , she has a pattern around her hairline and ears , and down her neck . " " ( ) Although the writers of DS9 were obviously aware of the physical differences between Odan and the Trill in DS9 , no canon explanation has ever been offered . In an attempt to explain the variations , Terry Farrell once suggested that the spotted members of the species were from the north of Trill whereas Odan was from the planet ' s south . ( " Cinefantastique " , Vol . 23 , No . 6 , p . 21 ) She also regarded the spots as natural - looking . " " It ' s not much different than freckles or leopard spots or zebra stripes , " " Farrell observed . ( Hidden File 05 , DS9 Season 1 DVD special features ) On DS9 , Dax ' s Trill makeup was regularly applied by Michael Westmore ; faced with having to select only one makeup to ordinarily apply , he chose the Trill spots , which pleased Terry Farrell and meant they spent a huge amount of time together . " " And it was a really exciting makeup , " " enthused Farrell , " " because makeup artists would always say , ' My god . How do they do the spots ? ' [ . . . ] And so , when he started doing it , I said , ' You know , it ' s really neat and I get a lot of compliments from you doing my makeup . " " ( " Crew Dossier : Jadzia Dax " , DS9 Season 2 DVD special features ) Westmore used brown make - up for the Trill spots , and subsequently accented them with burnt orange coloration . He applied the spots by hand , employing a technique whereby he deliberately made his hands quiver while painting the markings on . Westmore never used a stencil , so the spots were always unique . " " It ' s a laborious job , " " he remarked . " " There seems to be no easy way to make up a stencil for that . It just has to be done every day . " " ( " Cinefantastique " , Vol . 23 , No . 6 , p . 31 ) Farrell stated , " " Michael Westmore [ . . . ] [ used ] two different colors of watercolor . The first season we experimented with art pens , but they would take me two or three days to get off of my skin – not pleasant ! " " Applying the spots generally took slightly longer than an hour each day , though Farrell thought the process would likely have taken less time if she and Westmore hadn ' t enjoyed conversing with one another quite so much as they did . ( " " , p . 7 ) In hot shooting conditions , the sweat of the Trill - playing actors might cause the watercolor to run down the side of his or her face , so the actor had to be kept cool . ( " Crew Dossier : Jadzia Dax " , DS9 Season 2 DVD special features ) The disparity between Trills seen on TNG and the later Trills goes beyond makeup . In contrast to DS9 ' s depictions of the species , " The Host " seems to make it clear that the symbiont was dominant ( in fact , the symbiont is referred to as a " parasite " on more than one occasion ) , and that the host was merely a body with no influence over the joined entity . Odan was apparently unable to safely use the transporter , while Dax used it often with no trouble at all . Ronald D . Moore noted , " " The Trill were not supposed to go through transporters and we slid by it ( like the original Trill makeup ) . " " Furthermore , whereas Odan was ready to pick up where he / she and Crusher had left off , a Trill taboo against reassociation was , early in the series run of DS9 , suggested by Michael Piller . Trill society was foremost on Michael Piller ' s mind when he devised the ban on reassociation . " " He felt they ' d have to have a very strict taboo in order to avoid an aristocracy of the joined , " " reflected René Echevarria . " " Otherwise , they ' d all want to hang out with each other , their dear old friends from five hundred years ago , and it would become a really screwed - up society . " " ( " " , p . 279 ) DS9 appearances . Though " " ( p . 86 ) pretends the DS9 writers occasionally used a handbook called " Everything You Always Wanted to Know About Trills " , details about the species were actually established as and when required , such as for the DS9 episode . " " In this case , it was important to establish how difficult it was to get a symbiont , " " recalled Robert Hewitt Wolfe , who was credited with co - writing the installment . " " It said something about [ . . . ] the Trill culture that was interesting . " " The ad hoc method of inventing additional aspects of the species also resulted in the writers later revealing , in the DS9 outing , that it wasn ' t as hard to qualify for a symbiont as the Trill populace had been led to believe . Regarding the improvisational system the writers used to define the species , Ira Steven Behr commented , " " It ' s dangerous but fun . The whole Trill concept is very difficult , but ' Invasive Procedures ' dealt very successfully with it . " " ( " " , pp . 86 - 87 ) The notion of structuring the DS9 episode around a storyline about Trills , featuring Jadzia Dax and a Trill initiate , was suggested by Michael Piller . ( " " , p . 126 ) Jim Trombetta , who wrote the story , recalled , " " I had a little trouble writing that because I didn ' t really believe there was anybody that wanted to have a worm inside their body [ . . . ] [ The DS9 staff writers ] said , ' No , we ' ve gotta have it . It ' s an alien race ; it means something different to them than it does to us . " " ( " Captains ' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages " , p . 70 ) Ira Behr commented , " " I thought it [ . . . ] was an interesting show about Trills . " " ( " Cinefantastique " , Vol . 25 / 26 , No . 6 / 1 , p . 105 ) Another DS9 installment that features the Trill species is " Equilibrium " . Terry Farrell remarked , " " It revealed a lot about Trill society that we didn ' t know anything about before . The really big revelation was that about half of all Trills could actually be joined . " " ( ) For Robert Hewitt Wolfe , the opportunity to explore Trill society in that episode intrigued him . Wolfe especially enjoyed how the installment demonstrates that the Trill were meant to be considerably unpredictable and different from Humans . " " I think the culture is more complicated than that , " " he explained , " " and I think this show demonstrates that complication , which I like . " " ( " Captains ' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages " , p . 84 ) Ira Behr also approved of how the Trill were developed in " Equilibrium " . " " It ' s a fascinating subject . So fascinating it ' s deep waters to get into . I just love the scene with the guardian and the Trills – weird kind of stuff we don ' t quite understand . I also like a society that ' s basically medical . Its a bunch of people really involved in their bodies . " " ( " Cinefantastique " , Vol . 27 , No . 4 / 5 , p . 95 ) By DS9 Season 4 , the duration needed to apply the Trill makeup for Jadzia Dax had been reduced to forty minutes daily , despite the Trill spots still being done entirely by hand . ( ) In fourth season DS9 installment , a romance between two female Trill , namely Lenara Kahn and Jadzia Dax , was highly controversial both for the Trill in general , due to it being in breach of their taboo against reassociation ( the prohibition was first established in " Rejoined " ) , and for the viewing audience , as some viewers rejected the same - sex relationship as well as a kiss between the Trill lovers . " " Trills have no reason to be against same sex couples , " " Robert Wolfe remarked , " " but what a better way to show that they are a totally different , alien society than to see them reacting in self - righteous indignation just because they were lovers in a previous life ? " " ( " Cinefantastique " , Vol . 28 , No . 4 / 5 , p . 44 ) Never having played a Trill before , Lenara Khan actress Susanna Thompson consulted Terry Farrell with lots of questions about the species . " " She was very helpful to me , to give me the Trill background , to answer all my picky questions [ . . . ] She was quite open with all of that , as much as she knew , " " Thompson recollected . ( " " , No . 5 ) Farrell herself noted that , upon directing the kiss , Avery Brooks tried " to pretend we ' re not aliens in outer space " , instead concentrating on the emotional honesty of the scene . ( " Cinefantastique " , Vol . 28 , No . 4 / 5 , pp . 44 & 46 ) There is relatively a lot of exposition about Trills in " Rejoined " , for the benefit of viewers not intimately familiar with the species or the characters . Commented Ronald D . Moore , " " Not everybody knows Dax ' s family history , or what Trill society is about . " " Ira Behr remembered , " " We just wanted to make it clear that ' This is why this is going to happen , because we ' re not doing a show about " lesbians " , we ' re doing a show about " Trills " , and to make sure you know that , we ' re going to tell you what Trills are . " " ( " " , p . 280 ) For DS9 Season 5 outing , portraying the Trill spots called for extensive work by Michael Westmore . Explained Terry Farrell , " " Mike had to come in and paint them all the way down to my toes , ' cause I had a bathing suit on in that [ episode ] . " " ( " Crew Dossier : Jadzia Dax " , DS9 Season 3 DVD special features ) The " Star Trek : Deep Space Nine Companion " proclaims , " " Trills don ' t like heat , " " and observes that this can be seen when Jadzia Dax takes off parts of her uniform while on the surface of jungle planet Soukara in DS9 Season 6 entry . ( " " , p . 545 ) At the time Terry Farrell left DS9 ' s cast , Michael Westmore decided to no longer hand - illustrate Dax ' s unique Trill spots himself , though he ended up " detailing " Ezri Dax actress Nicole de Boer throughout the show ' s seventh and final season . ( " " , p . 594 ) When the character of Ezri Dax was invented at the start of DS9 Season 7 , Ira Behr also hit upon the idea that a newly joined Trill could be driven crazy by the previous lifetimes experienced by his or her symbiont . " " I just loved this idea of joined Trills being basically schizophrenic , " " Behr recollected . " " We ' d never played up the idea in the past , but it made sense . What must it be like to have all those voices and opinions ? ' Do I like " raktajino " or do I only " think " I like it ? ' It would give us all this wonderful stuff to play . " " ( " " , p . 593 ) While preparing to do a Los Angeles audition for the part of Ezri Dax , Trill society was one subject which Nicole de Boer questioned the production personnel about . " " I asked , ' What kind of people are Trills ? Was it an honor to be joined ? " " she recalled . ( " Cinefantastique " , Vol . 32 , Nos . 4 / 5 , p . 44 ) Trivia . Jeff Carlisle , who created a Trill Medical Diagram for the in - universe reference book " " , noted , " " I love the Trill . " " Even after both TNG and DS9 ended , Michael Westmore applied the Trill makeup one last time in , applying the Trill spots to Terry Farrell ' s face once again , for a " Star Trek " convention event called Dax 539 . Dating First Contact . It is not known when Trills and Humans made First Contact , but Tobin Dax once met the famous Cardassian poet Iloja of Prim while the latter was exiled on , indicating Trill and Vulcan had contact prior to 2245 . ( ) Emony Dax is known to have visited Earth in the mid 23rd century , where she was apparently close to Leonard McCoy . ( ) Travis Mayweather mentions having visited Trillius Prime , but it is not made explicitly clear if this is the same planet as the Trill homeworld . ( ) Apocrypha . A link between the Trill symbionts and the alien parasites seen in is suggested in the Pocket DS9 short story " Sins of the Mother " ( in the anthology " The Lives of Dax " ) and the novel " Unity " . This was expanded upon in " " . The neural parasite was first seen as it traveled in a comet passing close to the Trill homeworld . Audrid Dax and her husband , Jayvin Vod , went to the comet with a Federation team to examine it when Trill scanners showed a being similar to a symbiont in the comet . However , as the Federation was not yet aware of the Trill ' s symbiotic relationships , it was kept in secrecy . Upon coming into contact with the chamber of the parasite , it bonded with Jayvin , as well as the Vod symbiont , ultimately causing both of their deaths . The inconsistencies between TNG and DS9 Trill were dealt with in the novels by suggesting that ridged Trills and Trills who could not be transported were subgroups of Trill society ; both were mentioned or shown during the scenes on Trill , and the inability of some Trill to be transported was a plot point . The comics took a far different course , such as the " " mini - series , where both Odan hosts are shown without facial ridges but with spots . All Trills in the series are shown with the spots instead , no reasoning given . In another novel , " Forged in Fire " , the ridged Trills are said to result from a strain of the Augment virus that managed to infect a Trill colony through visiting Klingon traders . However , those Trills did not seem to be interested in working on methods of restoring the original Trill look , with this " sub - group " having recently ( at the time the novel was set ) being re - accepted back into Trill society . This division among the groups possibly explains why Odan was so different from other Trills encountered in the series . The novel also notes that the Trill avoidance of transporters was actually a means of avoiding the nature of the symbiote being disclosed rather than the process being dangerous to the symbiote .