What is a natural example of total internal reflection?

Answer 1

If you look at the surface of the water in an aquarium from the side of the aquarium with your eyes just below the level of the water, it will look like a mirror, and you won't be able to see anything above the surface. That's also true of a glass of water, but you can see the effect much more clearly with a container as large as an aquarium. Just make sure nobody jumps around or bumps into the aquarium or the table it is on because those vibrations will result in small waves in the water's surface and it won't look as good.