Betta and lasers.
I was 'playing' with my betta, Mandell, with various toys when my room-mate and myself accidentally discovered something amazing. He was shining his laser pointer to try and get the cat chasing my little betta toy (Which I use to induce flaring for photos). As he was shining the light he accidentally beamed it into Mandell's tank, and I noticed an interesting response. We then turned off the tank light and began shining the beam onto the tank decor, which led to the fish chasing it! It was so cute and I hope to get videos and photos sometime. I tried with my other fish but they don't seem to be interested at all. Mandy doesn't flare at it, just swims up and looks, very interested in the little red light, which is not characteristic of him. He is normally very violent, and flares at everything. Interesting, no?
It's really the eyes that get me. They aren't like goldfish or guppies, these guys can speak to you if you are willing to watch them and listen.