Have you ever been stung by a jellyfish? From the huge Lion’s mane jellyfish to tiny jellyfish larvae, jellies (which aren’t actually fish) can accidentally sting ocean swimmers with their built-in defensive mechanisms: nematocysts! Neosha S Kashef and TED Ed explain how a jellyfish stings in this fascinating video.

File under: vinegar. Related Australia-based information: Parent’s Guide – How to treat a Jellyfish Sting, with additional reading at Today I Found Out.

Related videos: There’s no such thing as a jellyfish, The Portuguese Man-of-War Up Close, and KQED Quest: Amazing Jellies.