History Trivia / DoctorWhoS7E4Inferno

** During the chase scene on the parallel Earth, Bessie's bumper gashed open stuntman Alan Chuntz's leg as it passed as he jumped out of the way a fraction later than he was supposed to. The gash was so severe that he had to go to A&E. John Levene stated on the DVDCommentary that "it was the worst wound [he]'d ever seen" and after Creator/JonPertwee saw the wound and learned he caused it, he became sick and almost couldn't carry on filming until a few hours later. Pertwee even went as far as buying Chuntz's wife a gift to apologise for the accident.

* ActingForTwo: Almost every actor in the cast plays two characters - one character in the normal world, and their parallel world counterpart. The only major exceptions are Creator/JonPertwee himself, since there is no Doctor in the parallel world, and Christopher Benjamin, who plays Sir Keith Gold in the normal world, since his parallel world counterpart is already dead when the Doctor arrives there.

* WhatCouldHaveBeen: Creator/KateOMara was considered for Petra Williams.

* CreatorsFavouriteEpisode: Both Creator/NicholasCourtney and Caroline John named this as their favourite serial.

** Sheila Dunn (Petra Williams) had previously played [[Recap/DoctorWhoS3E4TheDaleksMasterPlan Blossom Lefavre]]

* YouLookFamiliar: Derek Newark (Greg Sutton) had previously played [[Recap/DoctorWhoS1E1AnUnearthlyChild Za]].

* WhatCouldHaveBeen: The Brigade-Leader and Section Leader Shaw were to listen to a radio broadcast featuring Jon Pertwee announcing the progress of the drilling in a [[https://en.wikipedia.org/wiki/Lord_Haw-Haw Lord Haw-Haw impression]]; this was filmed but cut because the voice was too recognizably Jon Pertwee.

** Director Douglas Camfield suffered a minor heart attack after completing the location filming and the studio scenes for Episodes One and Two. This left Barry Letts to direct the studio scenes for the remaining five episodes. Fortunately, Camfield's preparations were so meticulous, he merely followed Camfield's plans.

** Originally, Section Leader Shaw was to interrogate the Doctor in part three, but Creator/NicholasCourtney, Douglas Camfield and Barry Letts thought that it should be the Brigade Leader. Caroline John wasn't happy about this.

* ActingForTwo: Stuntman Derek Ware did not actually perform the stunt in which his character, the mutated RSF Trooper Wyatt, having been shot, falls to his death from the top of one of the chemical tanks, in case he was injured (since he was also needed for the subsequent studio recording). His place was taken by Roy Scammell, who (ironically) also played the soldier who fired the fatal shot. Ware stated in an interview that Scammell had already signed the contract to do the fall before Ware had been cast as Wyatt. At the time it was filmed, it was the highest fall ever performed by a British stuntman.
** Any of the actors who appear as their real world characters and their parallel counterparts.

* CreatorsFavoriteEpisode: Both Creator/NicholasCourtney and Caroline John named this as their favourite serial.

* EnforcedMethodActing: The scenes on top of the chemical tank in episode two were not easy for Creator/JonPertwee, as he was afraid of heights. It took him fifteen minutes just to summon up the confidence to film the scene.

** Director Douglas Camfield suffered a minor heart attack after completing the location filming and the studio scenes for episodes one and two. This left Barry Letts to direct the studio scenes for the remaining five episodes. Fortunately, Camfield's preparations were so meticulous, he merely followed Camfield's plans.

* RealLifeRelative: Director Douglas Camfield's wife Sheila Dunn plays Petra Williams.
* TroubledProduction: Director Douglas Camfield had to withdraw from production after suffering a heart attack, leaving Barry Letts to finish the job. Fortunately, Camfield's preparations were so meticulous, he merely followed Camfield's plans. Then Creator/JonPertwee accidentally injured stuntman Alan Chuntz when he ran over his leg while filming the chase sequence. Pertwee felt so awful about the accident that he became ill himself, which threatened to disrupt filming.

* Any of the actors who appear as their real world characters and their parallel counterparts.

** A scene with the mirror universe characters listening to the radio was cut from the British broadcast, as the radio newscaster turned out to be too recognisable as Creator/JonPertwee doing one of his "silly" voices. The scene was included in the US broadcast, as it was thought that the audience there wouldn't be familiar with Pertwee's comedy work.

* YouLookFamiliar: Derek Newark (Greg Sutton) had previously played [[Recap/DoctorWhoS1E1AnUnearthlyChild Za]].

* WagTheDirector: Originally, Section Leader Shaw was to interrogate the Doctor in part three, but Creator/NicholasCourtney Douglas Camfield and Barry Letts thought that it should be the Brigade Leader. Caroline John wasn't happy about this.

* RippedFromTheHeadlines: Based on [[https://en.wikipedia.org/wiki/Project_Mohole a Russian attempt to do the same thing]], which was stopped suddenly, and nobody really knows why.

* YouLookFamiliar: Derek Newark (Greg Sutton) had previously played Za in [[Recap/DoctorWhoS1E1AnUnearthlyChild Unearthly Child]].

** DeletedScene: A scene with the mirror universe characters listening to the radio was cut from the British broadcast, as the radio newscaster turned out to be too recognisable as Creator/JonPertwee doing one of his "silly" voices. The scene was included in the US broadcast, as it was thought that the audience there wouldn't be familiar with Pertwee's comedy work.

* DeletedScene: A scene with the mirror universe characters listening to the radio was cut from the British broadcast, as the radio newscaster turned out to be too recognisable as Creator/JonPertwee doing one of his "silly" voices. The scene was included in the US broadcast, as it was thought that the audience there wouldn't be familiar with Pertwee's comedy work.

* WagTheDirector: Originally, Section Leader Shaw was to interrogate the Doctor in part three, but Creator/NicholasCourtney Douglas Camfield and Barry Letts that it should be the Brigade Leader. Caroline John wasn't happy about this.

* WagTheDirector: Originally, Section Leader Shaw was to interrogate the Doctor in part three, but Creator/NicholasCourntey Douglas Camfield and Barry Letts that it should be the Brigade Leader. Caroline John wasn't happy about this.

* DeletedScene: A scene with the mirror universe characters listening to the radio was cut from the British broadcast, as the radio newscaster turned out to be too recognisable as Jon Pertwee doing one of his "silly" voices. The scene was included in the US broadcast, as it was thought that the audience there wouldn't be familiar with Pertwee's comedy work.
** Another cut scene would've actually shown the death of the UNIT soldier mentioned by the Brigadier: Harry was to have come up behind him and strangled him to death.

** Another cut scene would've actually shown the death of the UNIT soldier mentioned by the Brigadier: Harry was to have come up behind him and either strangled him to death or broken his neck.

* DeletedScene: A scene with the mirror universe characters listening to the radio was cut from the British broadcast, as the radio newscaster turned out to be too recognisable as Jon Pertwee doing one of his "silly" voices. The scene was included in the US broadcast, as it was thought that the audience there wouldn't be familiar with Pertwee's comedy work.