Where could she have learned that?

A is in his "Why?" phase... everything anyone says to him is answered with a "Why?!" This is the source of many headaches for N, who really thinks a 2 year old should not question anything under any circumstances. I, however, deal with this with the age old reasoning of mothers... "Because I said so!" Actually, I try to give him a valid response, like "I'm cooking so we can eat dinner." ("Why?") "Because we need to eat good food to stay healthy." ("WHY?") and you get the point. Eventually, I reach the end of my knowledge or patience, and say "Because I said so!!!" Anyway... there is a point to this! Yesterday we are all in the car, N and I are talking up front, and we notice the kids are playing a game. It goes like this...
A~ Why?!
B~ I said so!
A~ (in a different tone) Why?
B~ (matching A's tone) I said so!
(repeat 20 times in different voices and the break into hysterical laughter)

I don't know WHERE she could have gotten that from!!!