A
hallucinogenic (read: poisonous)
mushroom hypothesized by Howard D. Fabing in the paper named below as an ingredient (along with mass or even - dare I say it -
copious quantities of alcohol) voluntarily imbibed by a fierce
Viking warrior to induce a
berserker rage of
bloodlust.
"On Going Berserk: A Neurochemical Inquiry." Scientific Monthly. 83 Nov. 1956 p. 232