My rabbits bum randomly twitches! Not the little happy twitch that they do when eating cecotropes or a delicious treat! It's like a rhythmic muscle spasm in his bum and tail muscle. Once I felt it as it was twitching and it actually feels like his whole tail muscle and bum muscle twitching. He looks kind of uncomfortable as it happens, not in pain more like he's waiting for it to pass? I'll try and attach a video! Update: won't let me post a video What is this???