I just have to tell this story about my 19 month old grandson.  If this incident is any indication, I'm afraid he is going to be a practical joker.  Today my wife had lain down to take her Sunday afternoon nap.  My son and his family always have Sunday dinner with us.  My grandson was sitting on the coffee table at the foot of our bed.  He had some little cookies he was eating.  My wife asked him if she could have one.  He picked up a cookie, got up and climbed onto the bed.  He crawled over to my wife.  He held out the cookie to her and said, "Pease, pease."  He wanted her to say please.  (We make him say please when he asks for something.)  She said please and reached for the cookie.  He immediately popped it into his own mouth!

I have to say this for him.  When he had one cookie left, he gave it to her.