Electroencephalography—trips off the tongue, doesn't it?—has been used to "read" the approximately 100 billion nerve cells in your brain for a century. But only now is someone using it for something really important: playing video games. The just-announced gizmo can even read facial expressions to see if, say, you laugh while killing an A.I. enemy; a response that will then be mimicked by your on-screen character. Just remember to resume quasi-normal behavior when you take the thing off.