A biologist, a physicist, and a mathematician are all watching a house that seems empty. Presently, two people enter the house, and after a while three people c

A biologist, a physicist, and a mathematician are all watching a house that seems empty. Presently, two people enter the house, and after a while three people come back out. The biologist says: "Clearly, there was a breeding." The physicist says: "Oh no, it's our measurements that are imprecise." The mathematician thinks for a while and declares: "If one more person walks in, the house will be empty again."