http://www.optillusions.com/dp/1-42.htm
I LOVE this magic trick. It's an optical illusion. You guys probably saw it done on a magic show on tv several years back. It's great for really fucking with people's heads who don't know what it is. So what you do is say it's an IQ test and tell them to look at it because only someone with a super IQ can stare at it without getting fucked up...