When attacked, the hagfish releases a slime that expands in the water in less than a second and clogs the predator's gills.
Why it is true
Glands along its body release mucus and ultra-thin fibres that unravel on contact with seawater, forming a gel thousands of times larger. Underwater cameras have filmed sharks letting go of a hagfish and swimming off, gagging on the slime.
Source: Scientific Reports (Zintzen et al., 2011)
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