Consider it like a "half flare." ;) You'll learn over time to read your betta's body language. I tend to think of those sorts of flares as being just more alert, but of course I am inserting my human thinking here, lol. Mine doesn't pop out the gill plate for everything; sometimes he just goes all puffy when he is stalking something outside his tank that he is curious about. I place things near him to keep him entertained. He does do a full flare though if he sees his reflection.