At the bank with Lisa:

Qatar: What are those boxes back there?
Lisa: They are safe deposit boxes.
Qatar: What are they for?
Lisa: People put their valuable stuff in them and then come visit it.
Qatar (incredulously) to the teller that has just returned: My mom says people put their stuff in those boxes in back and then come visit it.
Teller (confused): um, yes.
Qatar (almost laughing): What do they do, give them names and check up on them? How have you been Betty the necklace, everything okay? He goes on like this is the silliest thing he has ever heard.
Teller: I have never quite heard it explained that way before.
I suggested later that Qatar is old enough for a little Bourne.

That movie as well as being awesome, will teach him what a safe deposit box is for.