Trivia: Co-star Michael Madsen, whom also appeared in the first film, has stated his distaste with this sequel, especially in comparison to the original. He once referred to it in an interview as a "crock of s***."
Trivia: An early concept for the film was to make a more direct follow-up to the original's climax, where we see a rat become infected by the alien DNA. The film would have revolved around an army of alien-rat hybrid monsters that must be exterminated. This idea was eventually dropped in favor of a different script.
Answer: Nothing would happen to them. The restriction on sexual activity was to keep them from spreading any potential contaminants through bodily fluids. It's nonsense because there are plenty of ways to spread bodily fluids that don't involve sexual contact and 10 days seems arbitrary, but it fits with the overall erotic themes of the film series to have the quarantine specify no sexual intercourse.
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