In the area just after the electric zombies, you will see a few rooms with a glass cage by them. On the nearby computer, you can have the subject inside the cage undergo electricity, incineration, shrinking, zombifying, stretching, cranium-expanding, and thinning. If you power up the stretching or cranium-expanding too much, the subject will explode. There are two computers in single player and one computer in co-op mode.