No Doubles

There are no doubled ciphertext symbols in the eye messages. This is quite unlikely to happen by chance, so it's one of several indications that we probably have the right reading order. The expected frequency of doubles, assuming a ciphertext alphabet of 83 symbols, is 1/83, or about 1.2%. In messages as long as the eyes (1036 characters total, minus 9 because the last letter of each message cannot be a double with the nonexistent letter after it), using completely random values (which is similar to the IoC we see for the eyes), we'd expect to see about 12.37 doubles. So it's likely the mechanism specifically prevents doubles.