Drawing from an urn

Today's XKCD had a joke with an interesting linguistic angle:

I think this kind of humor illustrates two important things about words: First, you can't separate a word from it's associations and connotations. Second, those associations are different for different people in different situations.

For most English speakers, an urn is primarily a container for the ashes of a deceased individual, but for this teacher, in a discussion of statistics, it's just a container for randomized balls in an urn problem. But it's not a pun and these aren't homophones; both of these people are probably picturing a ceramic jar of some kind, they have the same core meaning for the word. It's just the clash of associations that makes the joke.

Language is a way of describing the world, and our understanding of the world is always affecting how we interpret it.