They don't 'bite the skin off'. They trim with a knife and then literally suck the blood off the penis tip. It has been known to cause venereal disease to infants. Orthodox (Kushners are) still do it like that.
https://www.youtube.com/watch?v=rLcXvgv4FYI
[–] 24977651? 0 points 1 point 1 point (+1|-0) ago
Not all Orthodox Jews still do it that way. Some just use gauze. The ultra-Orthodox, which the Kushners are not, are more likely to use the traditional method.