http://montypython.net/scripts/spam.php3


> A Mathematician, a Biologist and a Physicist are sitting in a street
> cafe watching people going in and coming out of the house on the
> other side of the street.  First they see two people going into the
> house.  Time passes.  After a while they notice three persons coming
> out of the house.
>
>
> The Physicist says: "The measurement wasn't accurate."  The Biologist
> concludes: "They have reproduced."  The Mathematician says: "Now if
> another person enters the house, it'll be empty again."
>
>        -Good Clean Funnies List
>         2000/08/31