I recently saw a chess match being played. After a few moves, Black was to move, and the board was exactly as at the beginning, except that the white king rook (at h1) was missing. How did Black capture it -- specifically, what was the actual move?
If knights are back in their starting squares (or if they have swapped squares) there have been an even number of moves. If Black is to move, White must have made an odd number of moves. Since the white knights made an even number of moves, the only other piece that could have moved (but not gone back -- that would also make an even number of moves) is the rook, that must have been taken in g1 without having gone back to h1.
The black knight that took it must have been at h3 (if at f3, White would have been in check) so the answer is Nh3xg1.