The tentacled snake Erpeton tentaculatum lives its entire life in fresh water where it feeds mostly on fish. Because the tentacled snake strikes underwater, the physical demands differ from those of air, and require modified methods of prey capture compared to terrestrial snakes. To examine this, we scored the feeding behaviours of five snakes and used multiple high-speed films of two snakes striking fishes. In the pre-strike phase, the snake usually assumed a J-shaped posture with its head turned posteriorly at the neck and its body held straight. The snake waited in such a rigid posture for the fish to move into the very narrow ‘window’ between turned head and body. Tentacles remained erected, and motionless. The strike was extremely rapid, occurring typically from pre-set J-shaped postures, not from sigmoidal body coils. As the head turned and travelled to the fish, the mouth opened and water collected in the ballooning throat. Significant suction feeding was absent. The fish was secured on buccal teeth and quickly swallowed by unilateral displacements of the jaws. Prey capture and swallowing exhibited specialized modifications of the general snake predatory behaviour to address the hydrodynamic demands of such an underwater strike.