Attachment of the rope to the harness is done using a knot called a figure-eight follow through, and often backed up with a stopper knot. Other knots are possible for the purpose, primarily a variation of the double bowline, but the figure-eight is usually preferred. Although it is harder to untie after a fall, it is inherently more secure, easier to tie, and easier to verify that it has been tied correctly. There are many variations of the bowline knot, and some will untie themselves when repeatedly stressed and unstressed, as is common in climbing.