A physicist, a biologist, and a mathematician are sitting on a bench across from a house

A physicist, a biologist, and a mathematician are sitting on a bench across from a house

They watch as two people walk in, and a while later three people walk out.

"The initial measurement was incorrect," says the physicist.

"They must have reproduced," says the biologist.

"If exactly one person goes in, the house will be empty," says the mathematician.