Humans have A, B, AB and O - what about horses?
Horses have 7 blood types - A, C, D, K, P, Q, and U. That sounds bad enough, but humans only have one factor - Rh - want to guess how many horses have? More than 30! You'd think the omnivores would be more complex ones.
Oh, and they develop antibodies to donkey blood too. Can't be simple, right?