Short answers, pulled from the story.
Hyoscyamus niger, commonly called henbane or black henbane, is a poisonous plant in the nightshade family Solanaceae. It contains hyoscyamine, scopolamine, and other tropane alkaloids that block acetylcholine in the brain, causing hallucinations, delirium, and in overdose, coma, respiratory paralysis, and death.
Henbane was associated with witchcraft and malefic practices from the Late Middle Ages onward, used in ointments, fumigants for conjuring spirits, and brewed into decoctions. A 1538 Pomeranian witchcraft trial includes a confession of using henbane seeds to affect the behavior of a man, and Inquisition records describe a woman strewing the seeds between two lovers with a spoken formula.
Henbane seeds were found in a Viking grave near Fyrkat, Denmark, first described in 1977. Researchers have proposed that berserkers may have used the plant to induce the heightened rage state they relied on in battle, based on analysis of henbane's intoxication symptoms.
Michael Schenck, whose account appears in Alexander Kuklin's book How Do Witches Fly?, reported physical discomfort, dramatically dilated pupils, a swaying perception of the mirror, and then vivid hallucinations of animals with contorted faces, clouds of mist, and a sky filled with herds of animals. He described being "flung into a flaring drunkenness, a witches' cauldron of madness".
Henbane was a traditional ingredient in gruit beer but fell out of use as hops replaced it across the 11th to 16th centuries. The Bavarian Purity Law of 1516 formally banned any ingredient other than barley, hops, yeast, and water, making henbane beer illegal in Bavaria.
In most Western countries, henbane material requires a prescription and is sold only through pharmacies. In the United States, henbane oil is not legally regulated and can be sold in ordinary shops. Cultivation for medicinal use is widespread and legal in central and eastern Europe and in India.