What has metal teeth and holds back a monster?

Zippers:

Before I begin, I have to first say that when I was seven another boy hit me with his jacket, and the zipper scratched my eye. If I didn't say this first then rest of the review would be colored with that negative experience. Now that it is known it has no power over me. According to my optometrist even the scar has faded, though he could easily be lying to me. But zippers, zippers! They are metal, and I believe the Platonic (which is to say ideal) Zipper is always brassy and yellow in color. They are found on pants, packs, pouches, and any number of other things whose purpose is to conceal and protect something that we wish to still access easily and often. Occasionally they twist and break, and in these instances they are not a zipper, they are only two jagged pieces of metal and a broken tool. And then they are frustrating. But only occasionally. Sometimes, as in the case of backpacks, there are two zippers on one pair of ziplines. In such case they can be augmented with tiny padlocks which bind the two zippers together, for protection from thieves. In this vein, sometimes pockets might have zippers to keep their contents from jostling out. I had such zippers on a pair of pants, once. I found them maddening. But as far as pants zippers are concerned, it's the ones at the crotch that are the most fascinating. Usually they're mere utility, a barrier to be crossed before pissing or defecating or an entirely solitary and boring removal of the pants in question. But sometimes they aren't. Sometimes a zipper is pulled by someone else, and for an entirely different purpose. I find something darkly psycho-sexual that before two people have sex there is this small ceremony of unbinding, unmaking. I prefer zippers to Velcro or buttons because of their determination to stay fastened. I say to a zipper, Stay zipped, and it is done. A button is only as good as the ever-weakening thread that holds it, and Velcro is loud and hard to get perfect. Zippers are quick and, adorably, onomatopoeia.

Zippers: 20/20. Occasionally they break, but, as I've said, they aren't zippers anymore and unworthy of discussion.