A laser can get trapped in water

A cool thing called “total internal reflection” happens when you point a laser beam at a jet of flowing water. To demonstrate this phenomenon, PBS Learning Media released a video in which a laser is positioned on one side of a clear tank of water. When the light travels through the water, it is slowed by the heavier particles in the water, effectively “trapping” the laser beam in the water. Even as the water flow is gradually decreased, the laser beam remains contained inside the jet, until it eventually disappears when the water is turned off completely.