Weird stuff happens when water hits hydrophobic substances. In this case, water and hydrophobic sand turn into a “liquid marble” in this video. It’s like watching the T-1000 get mobbed by fire ants.
When a single drop of water falls onto hydrophobic sand we expect to see the water get away clean. Instead it gets entirely covered in sand. According to the description:
“Because the sand is hydrophobic (rather than hydrophilic – which is typically the case), the water expands across the surface of the bed rather than penetrating into the gaps between the sand particles. During this process, the particles become stuck at the air-water interface to leave a particle-covered droplet. Such droplets are often called liquid marbles.”
I never get tired of seeing water droplets splatter apart on hydrophobic surfaces and then, uncannily, pull back together again like they’re liquid-metal terminators. Seeing one get surrounded and covered by little particles that seem to climb up its surface is even more amazing.