you can train them to flare on command if you like. take a thin-beam flashlight and a small mirror. hold the mirror up to the tank and as soon as he flares, flash the light. do this a few times a day for a week or so, then start trying it without the mirror, just flash the light. if he's caught on to the game, he will have a conditioned response and flare at the light alone.
i saw a video on youtube of a guy who taught a betta to jump back and forth between two bowls of water. i can't even fathom how long that took, or how long it's been since that guy was on a date :p