Reindeer, because of their size, are able to eat fly agaric without suffering ill-effects. Their digestive system removes the toxin, which means that their urine is not toxic, but does contain a high level of the hallucinogen. By munching on snow contaminated with reindeer urine, the Lapps realised that they could enjoy the effects of fly agaric without endangering their lives. How the Lapps learnt that reindeer urine is safe and fun was probably a matter of serendipity. Perhaps there was a snowball fight next to a reindeer corral, and maybe a Lapp who had the good fortune to be hit in the face by a urine-soaked snowball, swallowed some snow and started to hallucinate.
Having consumed reindeer urine, a Lapp's own urine would also contain the hallucinogen, and that would in turn be drunk by other Lapps. "There is evidence," according to Harding, "of the drug passing through five or six people and still being effective. This is almost certainly the derivation of the British phrase `to get pissed', which has nothing to do with alcohol. It predates inebriation by alcohol by several thousand years."
It is not inconceivable that during a fly agaric trip, a Lapp had a vision of a flying reindeer.
The other connection between reindeers and Christmas that Roger Highfield writes about is the notorious red nose. He points out that reindeer noses consist of elaborately folded turbinal bones covered with blood-rich membranes. This acts as a heat exchanger, warming up chilly air as it is inhaled, and then cooling it down as it is exhaled. Although reindeer noses reduce the loss of heat and water, the unusually warm and damp respiratory system provides an ideal home for a host of parasites, including 20 that are specific to mainland reindeer.
Odd Halvorsen of the University of Oslo, who wrote a paper about reindeer noses for the respected journal Parasitology Today, said, "It is no wonder that poor Rudolph, burdened as he is by parasites, gets a red nose when he is forced to pull along an extra burden like Santa Claus."