Children are good at pointing out to you things you may say all the time without realizing it. For example, I never noticed how often I said "Oh dear," until a sing-songy "Ah dee" popped up as a staple of Jane's just-over-a-year-old vocabulary.
The other day after Adam got dressed, he came and found me, put his hands on his hips, and queried, "Do I look like a million bucks?" And this morning after I got her dressed, Ellen started asking me repeatedly, "What I am?" It took a while for her to help me understand that the correct response to the question was "You look like a million bucks."
I'm pretty sure I picked up that one from Peter.