Its always interesting to me. That looks like its expelling some zooanthee and taking a poo, to me. The feeding tentcles will be short and white, and on the intersection of the ruffled outer edge and the smooth inner surface of the coral. I love brain corals. It may be just the photo, though it looks like on the top edges you are having some bleaching. Compare it to the first photo and see what you think. What type of lighting are you using? Steve