Since I'm in a rush, you get an easy one today...
During a chess game, Mary delivers a check, but her opponent's king does not move. Furthermore, no pieces block the check, and there are no captures. However, the game is not over after this move (not checkmate, stalemate, etc.). How is this possible?
Two possible answers:
(1) This is a correspondence game, and Mary sent a monetary check (cheque) along with her move...possibly to pay an entry fee or as a gift for her opponent. She did not "check" her opponent's king.
(2) They are playing take-me, or some other variant that does not require the king to be on the board.