In Through the Looking-Glass, John Tenniel’s two illustrations above are designed to fall on opposite sides of a single page. In this way the page itself becomes the looking-glass — Alice enters one side and emerges from the other, where all the details are reversed, including Tenniel’s signature and initials.
“Tenniel this time clearly draws the borderline between the world of dreams and reality,” writes Isabelle Nières. The dream occupies the center of the physical book. “Yet not all perceived that Alice’s return was not a symmetrical one, i.e. back through the mirror, but is symbolized by an almost perfect superimposition of the Red Queen on the kitten.”
(Isabelle Nières, “Tenniel: The Logic Behind His Interpretation of the Alice Books,” in Rachel Fordyce and Carla Marello, eds., Semiotics and Linguistics in Alice’s Worlds, 1994.)