Enforced Method Acting: Natalie Wood really did feel surprised when she tugged at Kris Kringle's beard, and saw him naturally react in minor pain.
Executive Meddling: The film was originally released in May despite being a Christmas film, due to an executive that believed people were more willing to see movies in May instead. This famously led to a marketing campaign that hid the Christmas themes of the film, including a trailer that instead of showing the film showed a fictional producer trying to figure out how to sell it while other contemporary stars raved about it. Fortunately, the film turned out to be a massive success anyway and actually ran long enough that it was still in theaters when Christmas actually rolled around.
In the original, the judge's political advisor is Fred Mertz. The judge himself is Peter "Pinky" Hartwell. Also, the prosecutor is Miles Archer. We also get appearances from a then-unknown Thelma Ritter (as a Macy's shopper) and Jack Albertson (as a postal worker).
In addition to the established character actors, the 1994 remake had Jayne Leeves around the time Frasier was starting, and Dylan McDermott of The Practice. It also has Allison Janney years before The West Wing.
Keep Circulating the Tapes: The 1973 made-for-TV remake has yet to receive a DVD release. However, it has become available for Netflix streaming.
Unintentional Period Piece: Which leads to a case of Hollywood Law in the 1994 remake when it sticks too closely to the original's story, as after 1975 it would only be necessary to prove Kris wasn't a danger to himself or others, rather than entirely disproving that he was mentally ill.