What are reindeers favourite food?

Amanita Muscaria (Latin) - Fly Agaric (Common Name). A mushroom of the amanita family which has a distinctive red cap and white spots.

Known to contain ibutenic acid and muscimol - chemical substances which produce an intoxicating delirious effect. So much do reindeer love this plant, they will drink the urine of other reindeer whom have consumed the fungi.