Ok, since I adopted Sox I have accepted that he sucks his thumb. He'll curl up with me in bed while I am trying to sleep and lay on my throat and just suck his thumb, or sometimes he'll prop himself up against my side and do it, I realize that this is a security thing and have brought it up when I first adopted him to some of cat-owner friends and they don't seem to concerned, should I be concerned that this habit is still taking place?