Jack has taken it upon himself to invent his own words on occasion. He will say something and use a word that no one in the entire world has ever used. At first I thought that I couldn't understand him, and asked him to repeat it, but then the word would change or be modified.
I think he does this because he is learning so many new words, he is experimenting with sounds, words and of course the reaction they get. (How long until he drops the "F-Bomb" I don't know)
I refer to when he is talking like this as speaking "Jackinese", his own little language and words. This way, Kate knows not to ask him a few dozen times to repeat himself so we can understand a word that has no meaning and is being elicited to get a reaction.
Another one of those little things that no one tells you about when you start raising kids.