Well, good to know if that were ever an opportunity for me. Probably would have to invent questions because it's hard to ask yourself out of being dumb-founded on the spot for the moment.

The interview for my current job had something simpler: something like finding random permutations, then what's the algorithmic complexity of this random algorithm. (It was years ago, I forget the details of it.) I just talked through the solution. That was nicer that having to come up with questions. :)