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At 16:24 words are on the film for a split second. It reads "Abyssus Abyssum Invocat". Considering the nature of the movie, don't say those words out loud.
Blink and you miss it: There are several phrases in latin scattered all over the movie. These phrases are shown in at least one frame:
15:54 min 'Abyssus Abyssum Invocat' (Deep calleth unto deep). These words are part of the Psalms, chapter 42, verse 7, of the King James Version.
44:45 'Facilis Descensus Averno' (the downward path to death/Hell Is easy), from Virgil's Aeneid, Book VI, Line 126.
55:07 'Cave Hominem Unius Libri' (Beware the man of one single book). A variant of 'Homo Unius Libri', a phrase attributed to Thomas Aquinas.
1:10:02 'Nihil Pretiosius Veritate' (Nothing is more beautiful than the truth), attributed to Francisco Sánchez de las Brozas, from his opus 'Minerva sive de causis linguae latinae', Book I, Chapter 1.
The language spoken by the two men next to the metal statue is Romanian.
For Antrum's occult aspects, directors David Amito and Michael Laicini studied various historical and cultural depictions of demons and the devil for inspiration, with their shared interests in religious imagery and the supernatural also factoring into the development of the film's script. Most of the symbols and runes depicted in the film were taken from a 17th Century text called Lesser Key of Solomon.
Antrum was developed by David Amito and Michael Laicini, during the development on a separate project, in which they were brainstorming possible scenarios that they could include in the film. The central idea, that would later become the basis for Antrum, came from the concept of what it would be like to watch a purported "cursed" film, which the filmmakers felt would make for a great horror film. For the film's occult aspects, Amito and Laicini studied various historical and cultural depictions of demons and the devil, while further inspiration came from a short film by David B. Earle titled Dining Room or There is Nothing (2006), which Laicini claimed to have seen while in film school.
The makers of the film purposefully did the editing to feature a new and equally different type of sound frequency that is rumored to have a negative effect on your nervous system.