We are driving to a 2:00 appointment
Oob (cheerily): It's 2:00!
Me (Panic! Look at the clock!): No, it's only 1:45, honey.
Oob (undaunted): It's 2:00! It says so on my invisible watch.
(shows me his wrist on which no watch is visible)
Me (long pause): If it's invisible, how can you see what time it is?
Oob (wiggling his eyebrows): X-Ray Vision!