The only known man-o-war jellyfish to float near the coast of the little seaside village where I used to spend my summers, stung my younger sister on her legs, side and her arm and hand where she tried to push it away. I got stung myself while picking the severed threads off her skin, so I know for a fact that jellyfish tentacles sting even when out of the water and not attached to the jellyfish any more. But the most hazardous thing came later, since I had to take my sister home and clean her skin with ammonia in order to neutralise the poison. Even today, my sister says those fumes were much much worse than the jellyfish sting!