I know we all live with turtles and we have seen what we have seen.
I have spent much time observing my turtles, and I can say with a lot of confidence that turtles are very complicated socially and there is a lot we still don't know.
However, whenever my turtles have fluttered at each other, it has always been over objects in the tank, whether it be rocks or plants or whatever. Sometimes, when they were much smaller, it was over space in general.
Typically, what I have observed is when Typhoon touches the big pink rock, Hurricane will swim over and start to flutter. Typhoon will either flutter back or give up and go away. Hurricane sits on the rock for a while, relaxes, and then goes about his/her business. They have never bitten each other after fluttering, nor have they bitten each other ever, period.
There are certain things in the tank that neither of them flutter over, and both use regularly with no problems.
Furthermore, because they are still hatchlings, occasionally when they flutter at each other, Hurricane will "sit" on Typhoon's back to show dominance. Hurricane is definitely the one in charge, and even though Typhoon doesn't challenge that or even care, like all animals Hurricane needs to make the point from time to time. This is a natural social behavior, and not to be confused for aggression.
We should be worried about aggression (attempting to harm each other) when we put two turtles in a tank that is too small and they have no privacy. Mine willingly spend a lot of time near each other, but they have the option to hide at opposite ends of the tank when they need to be alone.
I bring this up because it bothers me when new owners come in here, ask about fluttering, and ten people tell them to separate their turtles. Rather, we should be informing people about normal social behaviors, and how it differs from actual aggression.
