That's a yak

In Sunday School last Sunday, Finn's teacher was reading a book about creation to the class.  On each page she was asking the three kids to name what they saw.  Finn, of course, was full of his usual verbal eloquence.  On page describing the creation of the animals, Finn was proudly saying, "That's a giraffe.  That's a rhinoceros.  That's a hippopotamus."  Then the teacher pointed to an unusual-looking animal and said, "What about this guy?  I'm not sure what he is.  Maybe a bull?"  Finn proceeded to say, "No!  That's a yak."  Lisa and Diane (teacher) busted out in laughter, and Finn was embarrassed and wouldn't look at Lisa for the rest of the class.  Lisa still doesn't know where he learned about yaks, but maybe it was on the Y page of an alphabet book.