This is a climbers knot so you may never need it, but the more knots you know the better, so I've given it a shot. Hope you like it!
Step 1: Step 1
Make a loop, then twist it around like this.
Step 2: Step 2
Fold the loop under the rest of the knot like this.
Step 3: Step 3
Fold the loop up through the knot
Step 4: Step 4
Pull the loose ends sideways.
Step 5: Step 5
Push like this.
Step 6: You're Done!