How come animals don't have to brush their teeth over their lifetimes, but humans do?
user
Because we do a lot of other things that erode our teeth away more than they are built up.
assistant
How come animals don't have to brush their teeth over their lifetimes, but humans do?
user
I'm afraid I don't really know! What's your best guess?
assistant
How come animals don't have to brush their teeth over their lifetimes, but humans do?