Flip or flop

This little puzzle has deceivingly simple rules. But beware, the solution may not be so easy to find.

The playing field consists of twenty-five tiles. These tiles can be flipped one at a time, changing their colour from red to green. Your task, should you chose to accept it, is simply to flip all tiles. You have a free choice of which tile to start with, but after that each tile to be flipped must be a knight's move away from its predecessor. That is: two positions horizontal and one vertical, or one position horizontal and two vertical, as the knight moves in the chess game. To help you a little, a tile that can be flipped lights up when you move the cursor over it.

Don't get frustrated if you don't succeed the first time. Just click on 'reset' to start again from scratch.