The co-op in Dead Space 3 is designed to literally drive you insane. Player two will step into the shoes of Sergeant John Carver, who is suffering from the same strange form of dementia that Isaac suffered in the first two games of the series. This includes, but is not limited to: birthday parties, apparitions, and scenes of dismemberment. If you didn't know that, you'll probably think you're friend is a raving lunatic when he keeps pointing out the invisible toy soldiers in the room you can't see.