* ActorInspiredElement: During the credits there is no credit for costumes, this is because Creator/AudreyHepburn herself picked the clothes she wore from the stores in Paris. Creator/AlanArkin also claimed in an interview that he chose to play Roat as though he were "on every conceivable drug known to man," an element not original to the play.
* AwesomeDearBoy: Creator/AlanArkin said the role of Harry Roat was easy to get, as most of the actors approached prior didn't want to play a role that terrorized Creator/AudreyHepburn. Arkin said he jumped at the chance to play the part.
* BillingDisplacement: Although Creator/AudreyHepburn is given top-billing, she does not appear until over 21 minutes into the film.
* CreatorBacklash: The 1998 Broadway revival was not well-received despite excellent early ticket sales, with Creator/QuentinTarantino's turn as Harry Roat torn to shreds by most critics. Few of the cast and crew of this production are willing to talk about it, even decades later.
* EnforcedMethodActing: In regards to the audience. In some theatrical productions -- and even some showings of the cinematic adaptation -- ''every'' light, including those in the foyer, is either turned off or covered during the climax to make it harder for audience members' eyes to adjust and heighten tension.
* PlayingAgainstType:
** This was Creator/AudreyHepburn's only horror film, despite it more commonly being categorized as a suspense-thriller.
** The villainous role of Harry Roat is also extremely atypical for Creator/AlanArkin, who tends to go for more comedic parts. He claimed the experience of playing a villain was so uncomfortable that he never wanted to do it again and particularly hated "terrorizing" Audrey Hepburn.
* WhatCouldHaveBeen:
** Creator/JulieAndrews was considered for the role of Susy Hendrix.
** Jack L. Warner first considered Creator/GeorgeCScott for the role of Harry Roat and Creator/RobertRedford for the role of Mike Talman before casting Creator/AlanArkin and Creator/RichardCrenna in the parts.
** Creator/SeanConnery was mentioned in press as possible choice for role of Harry Roat.
** Creator/CarolReed was a consideration for the director position, but Creator/AudreyHepburn and her husband, producer Creator/MelFerrer, wanted Creator/TerenceYoung on the job since they were already friends with him.
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