The scene with Brandon Beckett playing video games was the very first scene filmed on day 1 of production.
The sniper bullet POV shots were mini drone cameras flown at the actors, hitting them.
When Lady Death is revealed in the forest near Thomas Beckett's cabin, it was shot in the middle of the night. Cinematographer Stirling Bancroft had to light up the forest to match the daytime shots.
The quote audi, vide, tace translates to see, hear, be silent.
In the restaurant when Donald South is dining with his young lady friend (Alyssa Barbara), the actress has arm tattoos, which had to be covered up after shooting the wide shots, to reshoot them later.