Teacher: Understanding gravity: Space-time is like a rubber sheet. Massive objects distort the sheet, and--
Student: Wait.

Student: They distort it because they're pulled down by... what?

Teacher: <<sigh>>

Teacher: Space-time is like this set of equations, for which any analogy must be an approximation.
Student: BOOOOORING.

{{Title text: Space-time is like some simple and familiar system which is both intuitively understandable and precisely analogous, and if I were Richard Feynman I'd be able to come up with it.}}