Female python twitching/shaking?

[Malkavian]

okay, I come home from school this afternoon to find my female carpet python has shed (hopefully pre-ovulation..) and is now moving around alot more than she has been since..oh..november or so. She's extremely feisty as usual (hungry I think) so i tossed her a rat, which promptly hid at the other end of the cage. Right now she's all riled up, howver I'm noticing something slightly unusual about her---when she rears back in "Don't tread on me" posture, her head and neck shake, much like a person's hands would if they've got too much caffeine. Never noticed this in her before, just wondering if its normal or nothing to worry about or what?