I'm a WHAT?!?

Today's conversation with the twins: 
B: Mommy is a cow!
Mom: WHAT? Excuse me!
A: A cow! Mommy is a cow! And Gama! Gama is a cow, too.
B: And Gapa is a donkey!
A: Uncle Tim is a pig! 
B: Daddy is a...a...a CHICKEN!!!
(Hysterical laughter)
Mom: What are A & B? 
(Silence)
B: We just kids...but big sister is a dog!!!

I swear...the only people who could call me a cow and still be walking...