"Free Trader Beowulf," the website Julia visits, is also the name of an iconic starship from the *Traveller* tabletop roleplaying game, first published in 1977 by Game Designers Workshop. (The connection is confirmed by the "#dnd/traveller" tag in the site's "Channels" list.)
The names of other users on the site are also literary references. "Failstaff" (with the woodcut avatar) is a reference to the fat antihero of Shakespeare's plays *Henry IV* (Parts I & II) and *The Merry Wives of Windsor*. "Asmodeus" (with the cartoon devil avatar) is the ruler of the Nine Planes of Hell in the *Dungeons & Dragons* cosmology. "Bender" (with the robot avatar) is the sarcastic robot of the *Futurama* cartoon series. "Menolly" (with the dragon avatar) is the heroine of a young-adult science-fiction series by Anne McCaffrey, beginning with *Dragonsong*.
The names of other users on the site are also literary references. "Failstaff" (with the woodcut avatar) is a reference to the fat antihero of Shakespeare's plays *Henry IV* (Parts I & II) and *The Merry Wives of Windsor*. "Asmodeus" (with the cartoon devil avatar) is the ruler of the Nine Planes of Hell in the *Dungeons & Dragons* cosmology. "Bender" (with the robot avatar) is the sarcastic robot of the *Futurama* cartoon series. "Menolly" (with the dragon avatar) is the heroine of a young-adult science-fiction series by Anne McCaffrey, beginning with *Dragonsong*.
When Penny is looking at the books which are titled with his friends' names, the red book to the left is titled "The Book of Mitch H. Engel" -- the producer of "The Magicians".
When Penny arrives in the Neitherlands, the cinematographer shoots most of the scenes using the Dutch angle. This means that the camera is tilted so that the horizon is not aligned with the frame. This off-kilter scene is used to imply/increase the viewers' feeling of unease.
Quentin refers to Alice as "Vix" when they are discussing how to have sex. A female fox is called a vixen.
The library and its librarians first appear in this episode.