Have you ever been stung by a jellyfish? If so, you’ll know that it really hurts. But how do they actually sting you? Well, as Destin from Smarter Every Day explains in this video, their tentacles have microscopic organelles called nematocysts which are basically like tiny hypodermic needles. If you graze their tentacles while swimming, the thread-like nematocysts quickly shoot out and then inject venom into your skin. The whole process is extremely fast and amazing to watch, and these guys managed to capture it in slow motion under the microscope. Check it out: