Two pieces of string meet one day in the park and while one goes on the slide the other goes on the swings. They're having a great time until one string decides to go on the roundabout.

After a while, the string feels really dizzy and falls off, scraping across the tarmac and making as tangled mess of one end and falling in a heap. The second string looked at him and sighed "you're not very good on that roundabout are you?"

The first string looked at himself and said "I'm a frayed knot".