Sagan Jokes

A couple of years ago, the following joke was told at a Mensa gathering:
Rene Descartes was sitting at a bar. The bartender came over and asked if he would like another drink. He replied, "I think not." And he vanished.
A another gathering some time later, a second part of the joke was noted:
Heisenburg was also sitting at the bar. After Descartes vanished in a puff of smoke, the bartender walked over to him and asked, "Did you see that?" To which Heisenburg replied, "I can't be certain."
This weekend, when I attempted to take this joke even further, we came up with a couple more people at the bar:
The bartender then noticed Einstein was there. So he asked him if he could believe what had happened. Einstein replied, "It's all relative."
Then the bartender noticed that Carl Sagan was there. He walked over to him and asked, "Can you believe that all these famous people are here in THIS bar?" Sagan replied, more...