Yes jellyfish can sting when they're dead, says Peter Richardson, and it’s down to the fact that a jellyfish’s body is about 95% water. Most jellyfish have tentacles covered in thousands of tiny nematocyst cells, each of which houses a bladder of toxins and a coiled ‘harpoon’ ready to fire when the surface comes under pressure.
If prey or an unfortunate human comes into contact with the tentacles, the surface of each cell floods with water, causing it to burst open and the weapon to launch.
When stranded on a beach and exposed to the wind and sun, jellyfish dehydrate, so don’t survive for long. However, if the tentacles are still damp, the batteries of tiny harpoons remain a painful hazard. So, look but don’t touch.