Euro Death-Knot
The flat overhand bend or “Euro Death-Knot” is widely used for joining two rappel ropes together. Because of its asymmetrical profile, the knot tends to rotate away from the rock. The flat side lays against the rock, which makes the knot pull smoothly across edges. To tie it, lay the two ends of the rope together, pointing in the same direction. Form the overhand knot in both ropes at the same time. Pull the knot tight, leaving long tails. Recommendations vary – most people suggest at least a foot of tail. Some people tie a figure-eight instead of an overhand. Some people use this knot for other purposes, such as joining two ends of a tied sling.
The failure mode of this knot is to invert flip / capsize / roll. This leaves topologically the exact same knot, just with shorter tails. You can observe this yourself. Tie a loose figure-eight knot and pull using a figure-eight makes it easier to flip. Youll have to help flip it around with your hands. If you do this enough times, you can make the knot roll all the way off the ends of the ropes, and youve got a failure.