John and Katherine's friends, Ivan and Merkie Ronan are played by Robert Curtis Brown and Jessica Tuck, who play Lucas Grabeel's parents in High School Musical 2.
Travis asks Daphne if she's heard of Dummy Hoy. Ryan Lane, the actor who plays Travis, played William "Dummy" Hoy in the documentary short 'I See The Crowd Roar: The Story of William Dummy Hoy.'
Dummy Hoy (b.1862 - d.1961) was actually real person, which his biography can be found on Wikipedia or other reliable sources.
The episode's title is a reference to the c.1936 painting "The Door to Freedom" by René Magritte. Note Magritte's "This is Not a Pipe" was the title of the pilot.