Oh, that's some small fish with a bony chip in their mouths, and if you do get bitten by a jellyfish, it's not as simple as a rash. The so-called red rash is actually an epidermal injury caused by the mouth of the fish, which has become inflamed after being soaked in seawater, and you should know that some of these little fish have mouths like files, which are so powerful that they can scrape algae from rocks and coral.