Yesterday in psycholinguistics I had a horrific moment. We were going over grammar, and eventually got around to explaining why there is an infinite possibility for new and unique sentences, when the dreaded word was mentioned:

Recursion.

My blood ran cold.

But rather than the mind-numbing explanation I have gotten before, the prof gave an example if "the house that jack built". I won't say that I fully understand now, but at least I have a sort of basic idea - better than I had before.