Go exploring by flashlight after the tank is well into total dark. You may see lots of life you didn't know was there.
That fellow is a good reason for wearing gloves when you move rock: if you get stung, you can be startled into dropping a rock, with all the potential for damage that entails. They won't hurt your corals, at all, and are extremely beneficial: I just had them save my tank from a potentially nasty nitrate spike by removing a huge dead snail in a single night. Your skin is, however, sensitive to them. And you may find the occasional fish with a slight case of bristles. I have a fool firefish that gets into a sleeping-spot quarrel with one now and again, and it gets a faceful when it bites the worm in question. They drop off after a day, with no damage to the fish at all.