That explains it.

(I pretend to talk into Tallulah's foot like it's a phone.)
T: Mommy, don't talk into my foot.
Me: OK.
T: I want to lie down and have you talk into my butt like it's a microphone.
Me: WHAT? No. I'm not doing that.
T: Yes, Mommy, it's funny! I want you to talk into my butt like it's a microphone. Like a veterinarian talked into that dog's butt. It was really funny.
Me: Where did you see that?
T: A veterinarian is a doctor for animals.
Me: Yes, I know. Where did you see a veterinarian talking into a dog's butt like it was a microphone?
T: It was a movie. On Cute Overload.