It's a hallucinogenic plant, specifically the root, commonly associated with witchcraft. It is a parasympathetic depressant, hallucinogen, and hypnotic drug.
Specific hallucinogenic images can be found on iamamiwhoami's Wikipedia page, and are as follows:
"the flowering humanoid, berries, and semen of a hanged man"
Sadly, recreational use of the Mandrake Root is limited due to the danger involved. Taken orally, the Mandrake Root is very harmful and potentially fatal. The only safe way to take Mandrake Root is to get the extract of it, turn it in to a lotion and rub in in low amounts on to key parts of the body. This troublesome procedure turns most recreational users to other, easier hallucinogens such as Peyote.
Sounds like a pretty unique religious/philosophical drug to me. Anyone?