Which one of these things is not like the other?

Which one of these things just doesn't belong?

Lets go inside and see...

Oh Moonie,

It's just you!

Silly horse, she thinks she's a cow.

Somebody had better tell her,

but not me, I don't want to hurt her little feelings.

Cause I'm nice & caring like that,

and if sweet Moonie wants to be a cow,

well then she should go right ahead and be one.