How do you tell an introverted computer scientist from an extroverted computer scientist?

Q: How do you tell an introverted computer scientist from an extroverted computer scientist?
A: An extroverted computer scientist looks at your shoes when he talks to you.

This is an occupational joke. The joke here is the statement that people who are computer scientists tend to be extremely introverted. The setup makes you believe that the answer will be a behavior that would show someone to be extroverted, however the answer is something that would show someone to be introverted normally. This insinuates that the introverted computer scientist is in fact more introverted than that, and either will not talk at all, or will look at his own shoes.

The stereotype that computer scientists are introverted is a very common one, probably because so many computer scientists are actually introverted (and also I would say because as a computer scientist you do not have to be a closet introvert).