So here's a fun concept. Trolls. Now, technically they not only supplied the bridge, but also maintained it. And they really only asked for recompense. Cross and pay, or find a ferry downriver. But, which does seem similar, a troll is one, online, who only reacts to someone crossing their metaphorical bridge. Pretty much those who wait for the specific word or phrase. But, they never give you a junction which you can use.