The Torah prohibits, generally, the infliction of a wound on yourself or someone else. See [Lev. 19:28](http://www.mechon-mamre.org/p/pt/pt0319.htm#28). The obvious exception is the commandment to perform a bris millah (circumcision) on a male convert or eight-day-old Jewish male. But from where do we find a justification to pierce a girl's ear or nose? I know that, in Rivka, we have precedent for piercings, but how is that justified against the commandment?