You remember back in grade school when you'd be trying really hard not to pee your pants and your "hilarious" friend would shake a water bottle or make whooshing water noises right by your ear? Yeah, not so helpful. But why?
It all goes back to the power of suggestion and conditioned responses, according to SciShow. Remember Russian physiologist Ivan Pavlov, aka the guy with the drooling dog? He was the master of conditioned responses. During one of his most notable experiments, he put meat powder in front of a dog to make it salivate (which is an unconditioned response, because #dogs). Next, he would ring a bell and feed the dog. It didn't take long for the dog to start salivating just from hearing the bell ring without the meat powder anywhere in sight because the dog learned to associate the bell with food.
Pavlov's pooch's conditioned response is very similar to what we experience when we hear a water faucet, stream, or that annoying friend making water noises: We've essentially learned to associate running water with peeing ever since our early days of potty-training.
Now please excuse us while we head to the restroom.