One day, a scientist looked at those jumping beans that get sold at novelty stores and thought, "I can do better than that." That's how the world got the "photosalient effect," or "photo-induced leaping" — or, better yet, "making crystals rupture themselves internally and jump around."
The photosalient effect may look like wanton destruction, but it actually has a possible benefit for humanity. Solar power cells right now can only use a certain range of light to generate usable power. This quest to make crystals burst their own insides so violently that they move came from a desire to make low-energy UV light, and perhaps even high-energy violet light, into something that can generate power.
When exposed to even a little light, these crystals can leap for millimeters . . . sometimes. As we see in this picture, sometimes the crystals leap while exploding internally but keeping their external shape. Sometimes they neatly break in two. Sometimes single, geometric shards break off of the main body of the crystal. And sometimes, just sometimes, the crystal shatters apart, suddenly and explosively. Not all of these reactions are equally helpful, but they are encouraging signs, in that they translate light into mechanical power.
To understand why, the best mechanical analogy is popcorn. When exposed to light the interior of the crystal rearranges itself suddenly and intensely. The outside can't quite keep up and there's an explosion. The explosion can make the crystal leap distances a hundred to a hundred thousand times its own size. If the crystal shatters during the process, photo-induced leaping is not a practical energy source, but one team of scientists have managed to find ways to make filaments just bend, not break, with the strain. According to them, "photosalient (leaping) solids can effectively utilize thermal or light energy and act as a robust and dynamically active "skeleton" to actuate sodium caseinate films as an elastic, flexible, biocompatible, natural protein matrix, similar to artificial muscle." Basically, we could make light-powered muscle fibers. Very cool, yes?