Page 189 - Geoffrey Budworth, Jason Dalton "The Little Book of Incredibly Useful Knots"

Constrictor knot

The constrictor is extremely useful when the need for a very tight binding knot arises, because

any pull that is applied to the free ends is then locked under its own tension. But because this
knot can be tightened so well, it is often nearly impossible to untie.

Start by making a complete round turn around the object. Cross the working end over in a second
round turn, on the opposite side from the first (1). Bring the working end to the front of the knot

(2). Feed the working end beneath both loops between the object and the line (3). By pulling the
two ends, this knot will become very tight, binding the object (4).