Hard to say. But it's nice to look at. From creator Daniel Stoupin, who spliced together 150,000 images for the video:
By day most hard corals are cute and colorful (more about coral colors). Their polyps coexist with their symbiotic algae and depend on light for nutrients produced by their photosynthetic symbionts. By night these polyps open up like flowers, but unlike flowers they turn into fierce predators, extend their tentacles, and sometimes invert their guts to digest the crap out of everything that they can reach. Coral colonies have to compete for substrate with other species, sometimes in violent battles. The winner is usually the species who digests faster or can resist digestive enzymes of the attackers better.
Gut inversion has never looked so pretty. [via]