The telepathic visions that Tuvok experiences in this episode mostly involves reused shots from the Scorpion (1997)/Scorpion, Part II (1997), in which Kes sees some of the same images. The recycled footage includes close-up views of a member of Species 8472 that both she and Tuvok individually envisage. Another reused shot is of the battle between a Borg cube and a Species 8472 ship, during which, in the far distance behind the cube, the Starship Voyager can also be seen. In fact, only one of the shots that, supposedly, Tuvok sees telepathically was created especially for this one; it shows a Species 8472 vessel being pursued by a Hirogen warship.
The Alpha Hirogen is played by Tony Todd, who played Worf's Klingon brother Kurn in Star Trek: The Next Generation (1987) and Sons of Mogh (1996). He also played the future Jake Sisko in The Visitor (1995). The other Hirogen Hunter is played by Clint Carmichael, who played the Nausicaan barroom brawler in Tapestry (1993).
The Hirogen claims his armor suit enabled him to go through the neutronium mantle of a collapsed star. To get a sense of what that means: the surface gravity on a neutron star is about 200,000,000,000 times Earth normal; the temperature is usually a few hundred thousand degrees; a tablespoon volume of neutron star would have as much matter as New York City.
The EV suits worn by Paris, Chakotay, Tuvok, and Seven are the ones used in Star Trek: First Contact (1996).
The intruder alert siren has a rare appearance in this episode, when Tuvok detects the member of Species 8472.