I remember reading that the Sami people used to drink the piss of a reindeer that had eaten fly agaric/fly amanita mushrooms since even though they're poisonous, most of the poison gets left in the reindeer while the nice hallucinogenic stuff passes through. Wikipedia put it a bit differently:

Patrick Harding describes the Sami custom of processing the fly agaric through reindeer.

Processing does sound nicer.