are able to shoot squirts of blood from their eyes, by rapidly increasing the blood pressure within the eye sockets, if threatened. Because an individual may lose up to 53% of blood in a single squirt, this is only used against persistent predators like foxes, wolves and coyotes (Canidae), as a last defence. Canids often drop horned lizards after being squirted, and attempt to wipe or shake the blood out of their mouths, suggesting that the fluid has a foul taste; they choose other lizards if given the choice, suggesting a learned aversion towards horned lizards as prey. The slime glands along the body of the hagfish secrete enormous amounts of mucus when it is provoked or stressed. The gelatinous slime has dramatic effects on the flow and viscosity of water, rapidly clogging the gills of any fish that attempt to capture hagfish; predators typically release the hagfish within seconds (pictured above). Common predators of hagfish include seabirds, pinnipeds and cetaceans, but few fish, suggesting that predatory fish avoid hagfish as prey. Communal defence In communal defence, prey groups actively defend themselves by grouping together, and sometimes by attacking or mobbing a predator, rather than allowing themselves to be passive victims of predation. Mobbing is the harassing of a predator by many prey animals. Mobbing is usually done to protect the young in social colonies. For example, red colobus monkeys exhibit mobbing when threatened by chimpanzees, a common predator. The male red colobus monkeys group together and place themselves between predators and the group's females and juveniles. The males jump together and actively bite the chimpanzees. Fieldfares are birds which may nest either solitarily or in colonies. Within colonies, fieldfares mob and defecate on approaching predators, shown experimentally to reduce predation levels. Defensive regurgitation Some birds and insects use defensive regurgitation to ward off predators. The northern fulmar vomits a bright orange, oily substance called stomach oil when threatened. The stomach oil is made from their aquatic diets. It causes the predator's feathers to mat, leading to the loss of flying ability and the loss of water repellency. This is especially dangerous for aquatic birds because their water repellent feathers protect them from hypothermia when diving for food. European roller chicks vomit a bright orange, foul smelling liquid when they sense danger. This repels prospective predators and may alert their parents to danger: they respond by delaying their return. Numerous