The Doors of Perception
As with most Marvel films, Doctor Strange features a cameo from the one and only comic book genius Stan Lee.
During a battle within the Mirror Dimension in New York, Stephen Strange gets flung into a bus, where we see the aforementioned legend reading a rather peculiar book.
Tis book is “The Doors of Perception” by Aldoux Huxley, which details the author’s experience with mescaline, a psychedelic drug. This, of course, is a direct reference to the film’s trippy visual effects, inspired by the illustrations of Steve Ditko.