Three pieces of string walked into pub.
The first went to the bar and asked for three pints of bitter.
The barman refused saying that drink only made pieces of string rowdy.
The second went to the bar and was given the same response.
The third ruffled the top of his stringy head and approached the bar.
"Are you another piece of string?" asked the barman. If so, I'm not serving you".
"No" the piece of string replied "I'm afraid not".
(a frayed knot)
