String in a Bar

A string walks into a bar and ask the waiter for a beer. The waiter says:

- I am sorry but we can't serve strings here.

The string goes home, ties himself in a knot, and messes up his hair. He goes back to the bar about an hour later, sits down and says:

- Waiter, give me a beer.

The waiter says:

- Hey aren't you the string who came in here earlier.

The string replies:

- No, I'm a fraid knot.