What causes a puppy to eat his own flesh.

I never heard of a dog eating his own flash. I wonder what do you mean by "eating his own flesh". You probably saw him licking a wound or something. This would be a normal behavior for a dog, to clean his own wounds. Or you saw him scratching himself with his teeth. This is also a normal behavior for a dog that has fleas. In this case, you should treat him against fleas.

By eating flesh do you mean you actually saw him take bites of skin off of his body at eat it??!! If so take him to the vet. I've never heard of that. Now if you're just talking about them licking their body constantly that's most likely because they have itchy skin and probably allergies.

In what way is your dog 'eating' its own flesh? You need to be more specific in order for someone to be able to help. However, I will try to help with what little information I've been given. Dogs lick themselves to clean or get off something that's bothering them. They also use their teeth in a scrubbing manner but they're not eating their flesh although it may seem otherwise. It's all perfectly normal as long as its a few seconds in doing the deed. Any longer than that means something is wrong with their skin and need help.

For me,this is really amazing. I have never heard of a puppy who eats his own flesh. Perhaps something is wrong with your puppy’s health. I think you should take him to the vet. I have also a feeling that mixed breeds often tend to get unhealthy. Nowadays, there are so many mixed breeds. Mixed look beautiful physically, but we cannot be certain about their health.