You really wouldn’t want to stand on one of these guys. Stonefish (genus Synanceia) are the most venomous known fish in the world, delivering an excruciatingly painful and potentially deadly venom to anyone unfortunate enough to stand on one of their dorsal spines. There are several different species of stonefish, but the reef stonefish (Syanceia verrucosa) is probably the most well-known. They’re incredibly well camouflaged, looking much like a rock or lump of coral, which is why it’s not uncommon for people to step on them.

The mode of action of the venom is poorly understood but it’s known to have cardiovascular and neuromuscular toxicity. Luckily for victims there exists an antivenom which reduces the likelihood of death, but until they seek medical help they will have to endure the agonizing pain that is rumored to be so bad that some individuals in the past have begged for amputation.

Although they look mean and ugly, their spines don’t appear that threatening until you see what is hidden underneath their skin. Check out this YouTube video from Smarter Every Day to find out more, and what it looks like when you milk one.