[OSWC2020 Day Seventeen: Superstition]
It's just a superstition, but it's far older than anyone remembers. Throw a slice of bread over the bridge or something will come for you. No one ever bothers to elaborate on what the something is. They never talk about what it will do to you.
The townsfolk abide by three rules. Don't ask questions, don't be too curious, and don't forget to give food to whatever lives under the bridge.
Lean over the bridge, look down, and you'll only see the river. You could stand there for hours and you'd never see anything move beneath the surface. You could crane your neck to look under the bridge and you'd only see the bricks holding it up. But the whole time you would have an unpleasant feeling that someone was watching you.
Some people may scoff at the superstition. They may insist it's nonsense. But even the most sceptical will still throw bread over the bridge. Just in case, they say. No need to tempt fate.