This knot is often used for stopping a rope from snapping when there is a fray. This knot only stays when the rope is being pulled from either side.
First off, make a 'S' with the rope making sure that there is rope left over on either side of the 'S'.
Make a loop at either end of the 'S' making sure that the loops goes underneath.
Put the curves in the 'S' through the loops and pull the both sides of the rope tight.
You have now completed the sheep shank.