Jack is my 4 year old tuxedo cat. He sleeps by my head on my pillow. During the night, he will wake me up with little whimpers. When I wake up and hear him, I automatically pet him, so as not to wake my husband. He has trained me well. He will start purring very loudly and then all of a sudden clamp onto my hand as hard as he can (all the while purring like he is having the best time). I actually have scratches that bleed because I try to pull my hand away and he just catches it with his teeth. I thought this was a sign that he wanted me to stop petting him, but when I do, he starts crying for more pets. Can someone please tell me why he is doing this and how I can prevent this behavior?