Shared with you
After the release of the Alien prequel Prometheus (2012), Sir Ridley Scott said that he felt that the Blade Runner movies shared a universe with the Alien film series, although this has never been officially confirmed since both franchises are owned by different studios. For a while, the Alien and Predator franchises (both owned by Fox) shared a universe, as shown in the Alien vs. Predator movies. In total, this meant that four different movie franchises (Blade Runner (two movies), Alien (first four movies), Predator (five movies) and Alien vs Predator (two movies)) shared a universe, for a total of thirteen movies. However, with the addition of Prometheus to the Alien series, serving as its backstory, the AvP movies were no longer being considered canon. This also excludes the Predator series from this shared universe, meaning that it consists of eight movies (two Blade Runner films and six Alien movies).
The blue laser lights that were used in the alien ship's egg chamber were borrowed from The Who. The band was testing out the lasers for their stage show in the soundstage next door.
The chestbursting scene was NOT filmed in one take (despite the myth). The scene was filmed twice: on the first take, the chestburster was unable to cut through Kane's shirt, so the crew needed to reset and shoot it again. The failed attempt is visible in the finished film, since director Ridley Scott thought it made it look like the creature was struggling to push its way out, and made the scene more violent (see The Beast Within documentary where this is discussed). According to designer Ron Cobb, the two takes of the scene were shot from multiple angles, and about 40 minutes of footage was available for screening.
Shredded condoms were used to create tendons of the beast's ferocious jaws.
According to Yaphet Kotto, Sir Ridley Scott told him to annoy Sigourney Weaver off-camera, so that there would be genuine tension between their characters. Kotto regretted this, because he really liked Weaver.
To get Jones the cat to react fearfully to the descending Alien, a German Shepherd was placed in front of him with a screen between the two, so the cat wouldn't see it at first. The screen was then suddenly removed to make Jones stop advancing and start hissing.