What actually happens inside an EpiPen when you slam it into your thigh? In this video, Steve Mould tears down an expired EpiPen (don’t worry, no good meds were harmed) to reveal the chain reaction of springs, plungers, and precision engineering that deploys the needle, delivers the adrenaline, and then makes the whole thing safe, all in one simple motion!

From hidden latches and compressed springs to a brilliant model, you’ll see exactly how Epipens work! Check it out!