Demongrass

Demongrass is the name given to an aquatic plant that grows in shallow areas near the coast. The plant's thorny vine-like stalks rise from the sea floor in a tangled mass that can easily entangle a passing swimmer or wader. As the victim becomes more entangled, they are stabbed and cut by the thorns, opening up deep wounds. Once someone is thoroughly entangled in demongrass, the only question about their fate is whether they'll drown before they die from blood loss. Some people who have had close encounters with demongrass claim that the plant moves with intelligence and malice to capture its prey, but most people write this belief off as a terror-inspired misinterpretation of natural movements caused by underwater current's and the victim's own movements.