Macaulay Culkin provides the voice of Elliot, the prank caller at the beginning of the episode. He calls in to the show saying the problem is that he is a salesman with a young voice, causing Frasier (Kelsey Grammer) to apologize, and Culkin replies, "Ha Gotcha Dr. Doufus". Macaulay's brother Kieran Culkin also plays the part of a caller during season 4.
Billy Kriezel (Mike Starr) was first mentioned as Frasier's (Kelsey Grammer) childhood bully in Season 1, "I Hate Frasier Crane" (1993).
The bathroom in Frasier's apartment will appear again a number of times later in the series, but look dramatically different.
When Billy Kriezel is recalling his acts of bullying to Frasier in high school, he mentions Frasier in his girls field hockey uniform. In Season 11 (Frasier Lite), we're told that it was Wayne Shafter who taunted Frasier about this.
Although it's a film set, and requires at least one open wall to accommodate studio equipment, Frasier's bathroom appears to be almost the same size as his living room.