Accidentally tarpitted prof's office hours by asking a question about one of the assignment problems. Turns out the obvious approach gives a non-physical result and he can't figure out why.
This sort of thing just follows me around, I'm not trying to cause trouble, I swear.
(If any physics nerds want details, I can give a description of the problem and why the result is non-physical, but I'll hold off on that until somebody asks.)