Bettas are so curious about everything. I think that's why they get into so much trouble.
I had a round plastic container holding vallisneria that had I put in my sorority. There was about 3-4cm between the gravel and the rim of the container, and about half my sorority swam in there and it was like watching a mouse on a wheel as they just went around and around and around.
Gorgeous females. Particularly the one looking up at the camera.