In this video, a laser is being shined through a block of plastic with changing density. At time 0:13, light enters the plastic and exits. The light takes the path the way it does because that path provides the least time to arrive at the current exit But why doesn't the laser also take another path to arrive at another exit below the current exit? Surely there is ANOTHER path of least time that would allow light to exit at another position? I imagine that instead of a laser we use a lightbulb, the whole block of plastic would be illuminated and each possible exit point would have light passing through it. What's up with a laser?