Xandy&Zak'sMum

3 pieces of string walk into a bar. First piece asks for a drink. The bartender says "Sorry, I can't give you a drink. You're a piece of string." Second string asks for a drink, and is also told he can't have one; he's a piece of string. Third piece of string unravels his end, messes it up and asks for a drink. The bartender says again sorry... no drink. You're a piece of string. To which it replied "A frayed knot".