i'm so sorry this happened! i know how you feel, because when i got sheeba i was hand raising some kittens and she accidentally got a hold of one of them and while she was trying to be "motherly" accidentally squished the poor baby to death while carrying it. i was so upset! have you checked the baby for a swollen tummy or something that would show that he might have some internal bleeding? he might just have some bruising since you said he's eating drinking and walking, that is maybe making him really sore. i sure hope the baby gets better!