Refract

that broken straw was never broken.

drag a beam across water — watch it kink, and the straw snap

The straw was never actually bent — light changes speed crossing from air into water, and that change in speed is what puts a kink in its path, which is what makes a straight object look snapped from outside. Push the light steep enough from underwater and past a critical angle none of it can escape at all — the surface stops letting light out and starts acting like a mirror.

Concepts: light, refraction.

An interactive you play with one thumb, on Wundr.