Incidentally, the urine of people who eat the mushroom [Amanita muscaria] constains substantial quantities of the isoxazole derivatives that produce the intoxicating effect. Impoverished Lapps knew this, and collected round the huts of rich Lapps who indulged in the mushroom at Christmas parties. When their overlords came out to relieve themselves in the snow, the serfs collected the urine to drink. When they, in turn, urinated in the snow, the reindeer fought to utilize what remained of the mushroom's intoxicating effects.

'The Last Word' --letter from Richard Platt (pg. 93)