Hagfish literally tie themselves in knots to escape a tricky situation – and that includes tying their bodies into complicated three-twist knots.

In many ways, hagfish are extraordinary. They are long, eel-like marine animals that carry far more blood relative to their body volume than any other fish , have four hearts – and only half a jaw .

It is partly because of this last feature that it is so useful for hagfish to tie knots in their long bodies. When the animal ties a knot at its tail end and slips it along …