Well, according to Accordion Guy these guys are playing Doom 3 and screaming in fright. You can get a link with the video here. I'm not sure I believe it, the guys seem to be hamming it up just a bit too much for the camera, and when I get scared in Doom 3 it's the "jump as something jumps at you unexpectedly" scared, not the "screaming like a little girl with her arm in a meat grinder" scared. It's amusing anyway.