One day I'll cease to be impressed by little games that acknowledge the existence of momentum transfer. That day is not today. Probably because I'm in a statmech kind of mood, and additionally because anything that strives to translate the laws of freshman physics into flash game form is a good time -- I'm up to 600 seconds. I should be tired of silly simple stuff like this by now...but I'm not. Hopefully there are other conservation-law based games out there. Please let lepton number be one of them.