A chocolate bar made up a rectangular array of squares has poison in its south west square. In a legal move, a player identifies a vertex and chomps off the chocolate lying in the northeast quadrant of that vertex, in such a way that some squares of the chocolate are moved. The aim of the game is to leave the opponent with only the poisoned square remaining. Show that the first player wins from a rectangular staring position. Can someone give me a hand?!

If the chocolate bar is square, then this problem is quite easy. For the other case(a rectangle which is not square), I huv no clue at all!