My son the comedian...

Daniel is developing a line is surreal jokes:

When is a man upside down and not upside down? When his house is upside down

When is a mirror not a mirror? When it is a sideways house

When does a foot have 5 toes and 2 toes? When 3 fall off in the bath.

I think he has the structure and the idea it has to be unexpected/wacky, but not the core of the concept...