Ball Python Growling Like A Dog?

So, Ralph was perfectly fine and I had handled him earlier this evening. All of a sudden I heard a strange growling noise (Like an angry dog). I checked in his vivarium and Ralph was striking at the thermometer, which is kept in the vivarium, and looked very angry. He made a lot of loud growling sounds. I was wondering what could have caused him to be so angry and make such strange noises. He has done a poop but I wouldnt have thought that would have made him so vicious. Thanks in Advance