Consider an 8x8 chess board with two corner places deleted, in opposite corners. Attempt to tile this board with 2x1 dominoes. Prove or disprove whether such a tiling is possible.
Naturally such a tiling requires exactly (64-2)/2=31 dominoes to do this, as each domino will cover 2 squares and each square must be covered exactly once. Anyway, yeah, its not too tricky.