Feeding (a la wikipedia)
Two Pacific hagfish actively feeding on a dead sharpchin rockfish, Sebastes zacentrus, while one remains in a curled position at the left of the photo.
While polychaete marine worms on or near the sea floor are a major source of nutrition, hagfish can feed upon and often even enter and eviscerate the bodies of dead and dying/injured sea creatures much larger than themselves. They are known to devour their prey from the inside. Hagfish have the ability to absorb dissolved organic matter across the skin and gill, which may be an adaptation to a scavenging lifestyle, allowing hagfish to maximize sporadic opportunities for feeding. From an evolutionary perspective, hagfish represent a transitory state between the generalized nutrient absorption pathways of aquatic invertebrates and the more specialized digestive systems of aquatic vertebrates.
In captivity, hagfish are observed to use the overhand-knot behavior “in reverse” (tail-to-head) to assist them in gaining mechanical advantage to pull out hunks of flesh from carrion fish or cetaceans, eventually making an opening to permit entry to the interior of the body cavity of larger carcasses. It is to be expected that a healthy larger sea creature would be able to outfight or outswim this sort of assault.
However, this energetic opportunism on the part of the hagfish can be a great nuisance to fishermen, as they can devour or spoil entire deep-drag netted catches before they can be pulled to the surface. Since hagfish are typically found in large clusters on and near the bottom, a single trawler’s catch could contain several dozen or even hundreds of hagfish as bycatch, and all the other struggling, captive sealife make easy prey for them.