The title and plot is an homage to the 1965 horror anthology film, Dr. Terror's House of Horrors, in which a fortuneteller uses tarot cards to predict the future of five strangers on a train.
The character "Howard" is a nod to author H.P. Lovecraft who wrote of ancient gods that often caused madness.
Harvey's reading has many ties to Howard Phillips Lovecraft stories. Among these are the name of the colony (Arkham), which shares its name with both the fictional town in New England that Lovecraft created and the publishing company Arkham House which specialized in publishing Lovecraftian fiction. The colony is located in Providence, where Lovecraft himself was born and lived most of his life. Also, Harvey experiences nightmares after coming to live in an old attic with a crooked ceiling, just like the protagonist in Lovecraft's Dreams at the Witch's House. He also was a roommate named Howard whose art is, in reality, depictions of otherworldly creatures, which is the plot of another Lovercraft tale, Pickman's Model. Finally, Harvey finds a secret window to another dimension in his roommate's closet, similar to the attic window appearing in The Music of Erich Zann.
When Nick sends Prudence he asks if she's ever been to the "Other Realm" which is how they used to refer to as the Witchy World in Sabrina the Teenage Witch