A programmer is at the airport with his wife,
she needs to go to the bathroom
so she tells him to stay there
and look at the luggage.
when she's back the programmer is counting the bags while scratching his head.
wife : what's wrong?
programmer : i don't get it. i was there, nobody took a bag, but i have missed one. we had 5 bags, but now we have only 4.
wife : how's that?
programmer : look: zero, one, two, thee, four!