Thank you for contacting Petco Pet Education Center, formerly Petcoach with your question about Rex. From the pictures, I'm wondering if I can see a bit of bone there, and it may be his mother bit off the end of his tail. It could also just be dry skin. If he is eating, moving around, and is going to bathroom normally, this can wait until Monday. If he is not eating, is very lethargic, and/or isn't going to the bathroom normally, you need to take him into an ER vet immediately. Best of luck.