The opening sequence "19 17 17 19" is peculiar. 19, along with 8, is the second most common number in the list. 17 is only half as common. You can’t have four vowels or four consonants in a row (unless the words are German) so either 17 is a vowel and 19 a consonant or the other way round. Since 19 appears more frequently (four times) in the message, it is more likely to be the vowel than 17 (which only appears twice). A is the most common vowel after E, so if he assumes that 19 is A, he gets