Junk in the Trunk

So the other day, Jaden seemed to have a messy diaper and I asked him if he had some "junk in the trunk."   He proceeded to repeat the word 'trunk' while I changed his diaper.  Today, he starts holding his seat and repeating 'trunk' again.  It made me laugh.  Yet, I can't get him to say 'yes' when I ask a question.