Propagation - fish & corals

I have been watching this coral for a few days now. I have a snail that I got in a few weeks ago, and it has all these spikes all around it's shell. It looks like a star. So, this one snail has been hanging out on the coral. I would move the snail, and then later it would be back. It has been going on now for a few days.

I don't know if the snail has anything to do with this, I just thought I would mention that. So night before last, I was checking out the coral pretty hard, and I ...