[svat]

The sentence is missing the example of "May", as you observed. It should say:

> Take, for example, "Day" and "May", which are even, and "Say", which is odd. Since the "-ay" suffix is consistent, it indicates that "S" is the first letter in the target word.

(Because as "Day" and "May" have the same parity and different from "Say", it must be that "D" and "M" must have the same correctness and different from "S", and as only one letter can be correct, that letter must be "S".)