About Poison Square
Poison Square is a mathematical game usually called Chomp. Two players share a bar of chocolate, taking rectangular bites from the bottom right. The last piece, in the top left corner, is poisoned. Nobody wants it.
How a match works
The bar has thirty-five squares. When you tap one, it disappears along with everything below it and to the right of it. Hover or press to see what a bite would remove. Bites get smaller as the bar is eaten away, and its edge becomes a staircase.
Eventually only the green square remains, and whoever's turn it is must take it and loses. The starting player is picked at random.
A curious fact
Mathematicians have proved that the first player can always win this game, whatever the size of the bar. The proof is clever and short, and it does not say how. For a five by seven bar, nobody carries the winning plan around in their head, which is why the game is still worth playing.
How to win
Learn the endgames, and steer towards them.
If only the top row and the left column remain, in an L shape, and both arms are the same length, the player who has just moved wins. Whatever the other player takes from one arm, copy it on the other. Eventually they are left with the poison.
So if you see an L with unequal arms on your turn, bite the longer arm down to match.
If two full rows remain and the top row is exactly one square longer than the bottom, that is also a losing position for whoever has to move.
Never take the square diagonally next to the poison early on. It leaves exactly the L shape, and your opponent will even up the arms.
Think of each bite as shaping the staircase. A minute a game, and plenty to discover, as the best small HTML5 games offer.