Knock, Knock?

Cade is really liking Knock-Knock jokes. It's all about the reactions he gets when he delivers the punch line, as is evidenced when he says, "Laugh, Grandma, you're supposed to laugh now" if my reaction is not robust enough. His choice of often nonsensical answers to the knock-knocks make his delivery even cuter. So, today, while we were in the car waiting for Isa to get out of school, I decided to use the jokes to get him to practice the names of relationships. Basically, the pattern was:
     Me: Knock, knock
     Cade: Who's there?
     Me: (name of family member)
     Cade: (name) who?
     Me: Don't you know your (sister, brother, etc.)?
Then I had him start the jokes so he would have to think of the relationship in the punch line. Well, he did one for Grandpa:
     Cade: Knock, knock
     Me: Who's there?
     Cade: Grandpa
     Me: Grandpa who?
     Cade: (pausing because he couldn't think of the right relationship, and then said:) Don't you know that guy you live with?

I laughed so hard I cried! Oh, my, three-year-olds are SO fun!