If you're ever snorkeling in the Indian or Pacific Ocean, look out for coral reefs looking back at you. You could be staring down a stonefish, the most venomous fish on Earth.
This stonefish was photographed in Indonesia, but its relatives live in shallow coastal waters from Egypt to Australia. They blend in with a variety of reefs and rocks — hence their name — and hide on the sea floor, waiting to ambush prey. But as a defense, they also have 13 sharp dorsal spines packed with a potent neurotoxin, which reportedly can kill a human within two hours. To avoid stepping on one, experts recommend swimming instead of walking in the ocean. If you must walk, shuffle your feet instead of taking big steps.