I occasionally stretch by putting my arms straight over my head, and then lowering them to horizontal. I end up in a position like this:
Every time I do this around my cat, she runs over and stares intently at my arms, waits for me to lower them, and then jumps up and tries to bite them. It doesn't matter if I move quickly or slowly (she'll wait).
I have figured out she won't pounce if I keep my arms tucked at the elbows and closer to my body, instead of straight out from my sides.
I don't get it! Do I look like something to hunt when I do that? Any ideas why that particular movement triggers a response?