The overhand knot is a stopper, especially when used alone, and hence it is very secure, to the point of jamming badly.

The overhand is the simplest of the single-strand stopper knots, and is tied with one end around its own standing part, its purpose being to prevent unreeving.

[2] As a defensive measure, hagfishes, which resemble eels, produce large volumes of thick slime when disturbed.

Hagfish also tie their bodies into overhand knots in order to create leverage to rip off chunks of their prey's flesh, but do so "in reverse" (starting at the tail, and sliding the knot towards the head for mechanical advantage).

If a flat ribbon or strip is tightly folded into a flattened overhand knot, it assumes a regular pentagonal shape.