Quote Originally Posted by WingedWolfPsion View Post
Most likely he was startled. I don't think thrashing is part of ball python courtship, they usually approach slowly, lol.
Not always true.. Some males will claim whatever area they are in and the mere sight of another snake will send them thrashing. My male cinny thrashes and flips around whenever introduced to a female. I have to always put him into the females tub and not the other way around. I would never even attempt to let him get close to another male. He would probably completely flip out.

In the case of the OPs snake there is no way to know what caused it. Im not sure if the snake could even see another snake in her arms if he was down in the tub. They dont have the best long distance eyesight. I guess its possible he saw what appeared to be another snake and thrashed. Just as its possible he was spooked after being left alone for a bit. Males will often fight and thrash with another male. Its more rare but its possible with a female. From that distance could he actually smell or see the snake well enough to know what it was? Who knows.