Trivia: A scene in which Sebastian brutally and graphically rapes his neighbor was filmed, but was mostly deleted as test-audiences felt it made Sebastian far too evil. And thus, the version of the scene in the theatrical cut only alludes to the idea without directly showing it. The original scene was reinstated in the director's cut released on DVD and Blu-Ray however.
Trivia: Whenever Sebastian is invisible and interacting with the other characters, Kevin Bacon's voice would be broadcast throughout several speakers randomly hidden throughout the set. This was done to make the reaction more genuine, since the actors would honestly not know where his voice was going to come from next, just as the characters would not know where Sebastian was.
Trivia: The infamous scene where Sebastian kills a dog was thoroughly investigated by the ASPCA - a non-profit animal welfare advocacy group. They reportedly felt the scene (despite being only shown in heat-vision footage) was so graphic, they suspected it might have been real. Director Paul Verhoeven ended up having to demonstrate how the scene was accomplished - star Kevin Bacon picks up a real dog, but through some slight trickery, was able to quickly switch it out with a realistic fake dog filled with stage-blood when he goes out of frame for about a second.
Trivia: The producers reportedly had to buy the rights to the 1992 novel "The Hollow Man" by Dan Simmons in order to name the movie "Hollow Man." The book is nothing like the film, instead being about a man who can hear other people's thoughts.
Trivia: Director Paul Verhoeven made the film because he wanted to make something more mainstream and palatable for wide audiences, given the overt violent nature and satirical tones of his previous films. He later stated that while he enjoyed working on the project, he feels it was a mistake because it wasn't a film that challenged him or spoke to his sensibilities, elaborating: "I think many other people could have done that. I don't think many people could have made RoboCop that way, or either Starship Troopers. But Hollow Man, I thought there might have been twenty directors in Hollywood who could have done that."
Trivia: The pool scene was one of the most complex to shoot, as traditional green and blue outfits didn't have enough contrast to be practically "keyed out" (aka removed digitally), as was done with other scenes due to the color of the water and background. Kevin Bacon's entire body ended up having to be painted pitch-black, as it was the only color to provide enough contrast for the digital artists to be able to practically remove him from the scene without having to go through and do so frame-by-frame.
Trivia: When Sebastian gets frustrated with himself in the lab, he stands up, walks, turns and beats his fist twice on the table. This is the same thing Kevin Bacon does in Footloose to his VW Beetle when he gets frustrated with the town.
Suggested correction: Presumably the military are interested because Sebastian's research could lead to advanced forms of invisibility technology, such as the ability to turn materials and weapons invisible for use in combat.
You cannot second guess the film like that. Sebastian is making no effort to make non-living items invisible and throughout the film we see that is not possible (why else would Sebastian have to walk about naked?). His research is on animals (and later humans) not "materials and weapons" and is based on their physiology, anatomy and metabolism. How would you inject a rifle or a tank with a serum? They don't have a bloodstream. The military wouldn't see any value at all in this research - maybe they would be interested in invisibility, but not if it was restricted to living creatures as we see here.
You know how easy it would be for an invisible person to infiltrate an enemy's compound undetected and take out powerful leaders or dictators? Especially if no-one knew the technology existed.
Easy? Impossible. First, they would be naked and unarmed. Too bad if you are trying to knock off Vladimir Putin - a taekwondo black belt - with your bare hands during a Moscow winter! Being invisible doesn't mean you can avoid making a sound or triggering a pressure plate or an infrared detector and so on and so on. Final answer - a naked, unarmed combatant would be about as useful as a chocolate teapot in any form of operation, covert or otherwise.