If the tentacles are noticeably longer and slightly more transparent than the rest as Sadielynn mentioned, the corals are within close proximity of each other, and they are reaching towards each other, it makes it seem like they are fighting. Maybe if you could snap a quick pic it might help clear things up.
To me it seems like they are fighting, especially if pieces are detaching and floating around; usually means they're dying. I have a relatively large hammer coral and it killed a frogspawn about 10" above it, some SPS
frags around it, and is now going for an Aiptasia anemone. I really don't mind it killing the latter of the bunch.