One of Peter's latest words is "ow".
He knows you say it when you get hurt but he seems to also like to use the word as an attention-getter or as a preemptive when he is going to do something to inflict pain (like hit his brother).
He rarely uses it when he is actually hurt, though during a car ride the following took place as I was turned around entertaining him (Brett was driving).
Me - Peter, where is your nose?
Peter - (pointing to his mouth) nose!
Me - No, silly! This is your nose (pointing to his nose), and mommy is going to steal it (pinching his nose to retend to take it).
Peter - Ow!
Just when I thought I was entertaining him, he goes and returns the favor... What a thoughtful son :)