when you don't pay attention to what your doing! I was reading a website that I find completely fascing who's initials are TCS, perhaps you've heard of it?
Gracie was begging me to pet her so I reached behind me and started petting her. I thought she felt a little strange, so I looked behind me on my bed where she was and I was very enthusiastically scratching her behind! Well, at least she seemed to like it!