Will you help me by playing my game? It's fun

Hmm, the stripping of exclamation marks in the title makes the "It's fun!" part a bit less.. fun.

Anyway, I have created this little game as part of my master's thesis. It's very simple, but it's a bit of puzzle. Some of you might see immediately what is happening, others might not be able to ever figure it out. I don't mind either way, but I'm trying to get some data before doing a thorough experiment.

I put it on Hacker News because it really is a puzzle, and most of my hackerish friends liked playing it (though some got frustrated). I hope you like it too!

very clever! It actually took me a couple of minutes to figure it out :D