Trick Effect & Routine:
A magician ties what appears to be an ordinary knot in a length of rope. He then makes the knot visably 'melt' away.

Preparation:
Get an ordinary length of rope, but not too small.

Method:
Hold the rope at the right end with your right hand (I shall call this end A). Hold the rope somewhere near the middle with your left hand. Move End A inwards with your right hand, creating a loop. Hold the rope where the 2 bits cross with your left hand. Put your right hand through this newly created loop, and grab End A. Pull End A back through the loop, and don't let go with your left hand. Pull End A tight. You should now have 2 sort of rings around your left thumb. Remove that thumb. Using the left hand, pull the rope crossing nearest End A leftwards, so the knot is tight. You should now have a slip-knot that looks very real. Give the knot some magic (ie a blow, or a pass, or some words) and give the rope a sharp tug. The knot shall dissolve away.