The southern Ontario indigenous legends of Ekarenniondi and Oscotarach are referred to in this episode. Ekarenniondi was the name given to a rock which marked the path leading to the afterlife, which was referred to by local natives as The Village of the Souls. Along this path was the cabin belonging to Oscotarach ('Pierce-Head'), who drew the brains out of the heads of the dead, and kept them. (The tale might sound gruesome, but Oscotarach was seen as a benevolent helper who removed the memories from the dead so that they would not recall their past lives or long for life itself.)
The "Cursed Caves" of Ekarenniondi were formed about 450 million years ago, and can be found at 260 Scenic Caves Road in the town of The Blue Mountains, Ontario - near Collingwood and the Blue Mountain Ski Resort.
This episode is set around Hallowe'en, 1907.
At about 39:30, Murdoch mentions "Archean rock". The Archean eon is the second-oldest eon in geologic time. There are no rocks (only minerals) and no fossils from the first eon, the Hadean, so Archean rock is the oldest rock on Earth, from about 2.5-4 billion years ago.
Dr. Ogden identifies the mushrooms that Henry ate as 'Psilocybe semilanceata', which is found all over Europe, Turkey, Pakistan, and North America (including Ontario). The first reliably documented case of intoxication by this mushroom occurred in London in 1799.