Im not sure what my brain coral has going on here but its interesting. It doesn't look like it is in distress or anything but it kinda looks like its feeding on the rock under it. Here are some pictures
I see you have it sitting on rock. Sometimes rock can irritate the flesh. Not saying that's what is happening but I prefer to keep mine on the sand. He totally looks happy though.
I have had him on a rock pretty much the whole time I have had him. He seemed to get irritated by the sand more than the rock. Plus the sand blows around a bit in my tank so I was having to blow it off of him all the time.
I guess ill just keep an eye on him for any sign of stress.
There may have been something irritating it at the base, maybe something that was on the live rock, and the coral engaged in some digestive warfare with it. Did you look at what was going on underneath the whole thing or just leave it in place? Probably best not to move it, but I would be curious to know if it have exuded more mesentery at the base.
I left it. I didnt want to mess with it and possibly hurt it. I think there may have been a spaghetti worm on the rock so maybe they were fighting it out. I moved it from it last spot because the tank is getting a little crowded and needed the space. It had grown quite a bit and started fighting with my duncans.