Fish have body language all their own
Betta are easy to read if you spot the signs......especially the heavy finned males when in a community setting. The curling of tail and finnage around food to stop tankmates eating, the snapping back as another fish swims quietly by but too close, the way that after a while tankmates get nipped and pushed around, and how tankmates cower as far away as they can from the Betta and often turn their back on it when it swims by.
Watching the fish you can often pick up behavioural traits of your fish, how different individuals react to you and each other. Fish can be quite fascinating...if a little painful at times when they decide your flesh is better than the food you are serving them