Possibly the first in a series?
Zippers are pretty damn common. Hell, you probably have one close to your body right now! They're really quite interesting pieces of technology, yet we take them for granted so easily. You can probably make a decent guess as to how they work though, so I'll be telling you something new about them. Note that this mechanism isn't present in all zippers, but I do see it every now and then.
Did you know you can lock some zippers? You probably already do it, actually. Some types of zippers have this little mechanism, that makes it so that the zipper can't move if the tab lays flat down against the line of teeth. When you rotate the tab so that it stands upright, making about a 90° angle with the line of teeth, it pushes up a small component in the slider, which releases the lock. Rotating the tab back down again re-locks it, so that it can't accidentally slide open!
When I first discovered this I was like "holy shit that's awesome" but then noticed the zipper I had on my hoodie that day didn't have it. A few days later I noticed another zipper did have it, and I was so amazed by how they put such a seemingly complex mechanism into an already pretty amazing little product.
Zippers are you friends, just be careful not to get any skin stuck in 'em!