Watched by a computer scientist, a biologist and a mathematician, a man and woman enter a house. A little later they see three people come out. The two scientists are each puzzled for a while but then the biologist, suddenly looks really happy and, exclaims “They must have reproduced”. The Computer Scientist, also looking pleased with herself, says “Ahh! there was a bug in the original counting algorithm – an initialization error”. The mathematician, however, has been unperturbed by the whole thing and just remarks “If another person goes into the house, then the house will be empty.”