There is mould under every bridge. Seeping into foundations, winding through brick and around rebar. It isn't on the blueprints and definitely violates regulations.
When someone crosses the bridge, heading home from work or on an early morning jog, the mould whispers. Like a spore, an impulse drifts into their head. They're called intrusive thoughts—what does the intruding?
The whispers win. A nervous glance at the water below, and then they hop the railing and disappear into the river with a splash. The body is never found. It vanishes... or perhaps it's consumed?
There is mould under every bridge.