They do have strong jaws but small teeth. It hurts to get bit but its not as bad as other reptile bites I had. One thing your friend could try which may break him out of the habit of biting (unless the vet finds a medical reason for it) is have her wear heavy gloves..even an oven mitt and let him attack it. It won't hurt his teeth and he will see biting it isn't making it 'go away' so he should give up after awhile...especially since it goes away on its own.
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PHLdyPayne