This marks the first episode in which the Janitor interacts with any main cast member other than J.D. (After harassing J.D. as usual, he tells off Turk for being with him.) The writers had originally toyed with the idea of revealing the Janitor to be a figment of J.D.'s imagination.
As Elliot unleashes into a fast-paced monologue explaining why she's insane to Paul, she brings up how she talks to her cat(s) - mentioning both singularly, and then plurally in the following sentence (saying they respond in her mother's voice). Elliot's cat(s) is/are never actually seen, nor mentioned before or after this episode.