DS4 does that from time to time, he used to do it more several months ago. Sometimes he will make up words and instist that they are words, sometimes he will make up a word and then tell me "that means _________ in Spanish" I minored in spanish so I can usually tell when he is making stuff up. Lately he is into making up expressions and insisting they are expressions. He was sick this weekend and said to me "mom I am really topped" Apparently that means that he is really exhausted and not feeling well. He makes expressions up all the time, but he generally doesn't use them more than once so I never know what he is talking about. He always insists "It's just an expression mom." He has made up some interesting expressions. Who knows....maybe I will hear others saying them eventually. And also, my DS really enjoys foreign languages and knows quite a bit of Spanish. That can be really fun with kids like this. Or introducing a word a day.