Okay.The answer is simple, John and Mary are the names of the two gold fishes in the fishbowl. They're dead because the cat accidentally knocked the fishbowl over.The only the other thing inside the room was a cat.And everybody busted out laughing.Mogami.The glass fragments of the fishbowl were scattered all over the room.So what killed John and Mary?"I can't think of anything, Hyuuga-san."So when you entered the room, John and Mary were lying on the floor, dead.
