Did you know that when you attack critters there is a slight delay between them being under attack and them getting one-shotted? In this time we can learn a little bit about them.
Rats and snakes run away.
Roaches fight back, for one damage.
If you happen to find a school of fish, there are some swimming near Sen'jin, they will also fight back.
The plagued insects from the Stratholme gates have strange behavior as well. If you run through the gates fast enough, some will still aggro. However, you can get pretty far away because they're slow, and I have rocket boots. They will chase you. The strange part is that not all will aggro on you, but they will still follow.
This same behavior can be found in Botanica. The first boss walks back and forth along the raised area. She also will periodically walk over and talk with the trash before her. If you happen to pull them as she is going over to them, but before she is close enough to socially aggro, she will continue to walk over to it, even as it chases you across the room.
I wonder what causes that.