I’m re-reading the old BBFC report on Alien from 1979 and one of the interesting things to emerge from it is how people who had only seen the creature in the first film (and only watched it once) felt that it was constantly growing and changing form throughout the film. There were only two designs used (the chest-burster and the full grown creature) but the way the creature was shot, edited and performed conjured so much more in the minds of the viewers at the time.