Title speaks for itself. I had this happen to me on two separate occasions by two different women last weekend and I'm struggling to figure out what it means.

The first time it happened I was getting drinks with some friends at a local bar. I was sitting at a booth talking to my friend across from me when a girl who is a mutual friend sat down next to me. I don't really know this girl to well and I am not particularly interested in her. Without saying a word she starts scratching and rubbing my back, almost like you would a dog. I was pretty confused and gave my buddy the "WTF is her deal" eyes. I chatted with her for a minute, mainly to figure out her angle, which was clearly to be around me. Trying to be polite (and try my luck with her significantly more attractive roommate) I excused myself and went on with my night.

The next time sort of thing happened to me was later that night. I was at a different bar where we had met up with another group of friends. I was sitting on a couch and a girl I am interested in sat down next to me. I had had some chemistry in the past with this girl but she currently has a boyfriend. Just like the girl before, she started rubbing and scratching my back as she talked with me. Knowing she had a boyfriend I was cautious when trying to escalate with her, and and regardless she didn't seem too receptive.

Anyways my question/confusion here is what the heck does this back scratching mean? Is it a indicator of interest? Some kind of girl-kino witchcraft? From one girl it clearly means she is interested, however another girl it means something totally different. Thanks for any advice y'all