It is caused by a discharge and is totally normal when you get any type of sexual contact. It happens when you get a pleasure....basically PLUS I DON'T SEE Y PEEPS HAVE TO PUT SO MUCH CRAP ON THE ANSWER ALL I WANT IS THE FRIKIN ANSWER jeeves!!!!!

Go on eBay there are loads and they are getting cheaper by the second. Just type in Nintendo WII and up they come (pop) :)