If sardines produced a horror film, the vicious serial killer would be a sailfish. Sailfish (Istiophorus platypterus), named for their sail-like dorsal fins, brandish elongated knifelike bills and swim at speeds up to 110 kilometers per hour—12 times faster than Michael Phelps. The function of the pointy bill eluded scientists, though some argued sailfish wield the appendages as a weapon when hunting schooling fish. To test this idea, a team of researchers plunged into the open ocean and recorded over 4 hours of sailfish stalking and preying on schools of round sardines (Sardinella aurita). Analyzing their footage frame by frame, the team compiled the first direct evidence of sailfish using their bills to attack prey. In the above video, a sailfish corrals the sardines into position before slashing through the school with its sharp bill, gashing several fish and creating a cloud of torn scales. The slicing attack employs one of the highest accelerations ever recorded in an aquatic vertebra and is nearly impossible for the sardines to dodge, the team reports online today in the Proceedings of the Royal Society B. The team also spotted sailfish stealthily spearing individual sardines without alarming the rest of the school. By injuring their prey first, the team found that sailfish increase their odds of a successful hunt more than threefold and earn their place as the ocean’s slasher stars.