Meet the humble hagfish, an ugly, gray, eel-like creature affectionately known as a “snot snake” because of its unique defense mechanism. The hagfish can unleash a full liter of sticky slime from pores located all over its body in less than one second. That’s sufficient to, say, clog the gills of a predatory shark, suffocating the would-be predator. A new paper published in the journal Current Biology reports that the slime produced by larger hagfish contains much larger cells than slime produced by smaller hagfish—an unusual example of cell size scaling with body size in nature.

Hagfish slime is an example of a non-Newtonian fluid, in which the viscosity changes in response to an applied strain or shearing force. … Applying a strain or shearing force will increase viscosity—in the case of ketchup, pudding, gravy, or that classic mix of water and corn starch called “oobleck”—or decrease it, like non-drip paint that brushes on easily but becomes more viscous once it’s on the wall.

Hagfish slime can be both. It turns out that the suction feeding employed by many of the hagfish’s predators creates a unidirectional flow. The elongated stress of that sucking flow increases the goo’s viscosity, the better to suffocate said predators by clogging of the gills. But when the hagfish is trying to escape from its own slime, its motion creates a shear-thinning flow that actually reduces the viscosity of the slime, making it easier to escape. In fact, the slimy network quickly collapses in the face of a shear-thinning flow.

Lots more exciting, thought-provoking analysis like this in the article.

As a youth, our family fed ourselves significantly by coastal fishing. I caught a hagfish – once! I wish I hadn’t.