My betta goes to hang out near his thermometer a lot. Took me a bit to figure out why, but I noticed one day he was 'looking' at the thermometer, not flaring, just looking, like bettas do. After looking at it myself a bit, I noticed I could see his reflection clearly (albeit, distorted) in the glass! Turns out he just liked staring at his distorted himself, or maybe he was wondering why there was a betta that looked like him stuffed in the thermometer. xD
I had to laugh when I realized. Haha.