Q: Did you hear the joke about the roof?
A: Never mind, it’s over your head!

Explanation: “Over your head” can have two different meanings: 1) something is literally above you; 2) something is too hard for you to understand.  For example: 1) the ceiling of the room I am in is over my head and keeps the snow off my shoulders; 2) Quantum physics is “over my head” because I do not understand it.

This joke plays on the double meaning of the phrase “over your head.”  Get it?  Or is it over your head?