Hagfish evade predators by churning out vast quantities of slime to slide out of their grasp. Their slipperiness and lack of spine makes it easy for them to tie themselves in a literal knot, which can help with this evasion, but they also do it when not being harassed—for fun, maybe. Wikipedia says they form an overhand knot like a pretzel, but the only footage I’ve seen clearly shows a figure-eight knot, as here. I think they’re cool. They’ve existed virtually unchanged for hundreds of millions of years, like our friend the horseshoe crab, and what’s with having a skull but no spine???