Ridley Scott's Alien features one of the most underrated plot twists of all time, and it was actually foreshadowed at the start of the film. As the crew are about to leave the Nostromo to investigate the distress signal on LV-426, Ash is shown somewhat jerkily jogging on the spot as though he is warming himself up. While this may seem like a minor detail in the film, it becomes all the more significant when it is later revealed that Ash is a robot under orders to return the Xenomorph to Earth.
During the Alien DVD commentary, Ridley Scott reveals that Ash jogging in place was an idea by the character's actor, Sir Ian Holm, stating it is "The first sign here that Ian isn’t necessarily what you think he is. Is he arthritic, or is it something else? Or years in space have got to his ts. That was a little suggestion by him which I thought was great… an actor really thinking through the whole idea and getting into the notion of the realities of science fact and not science fiction." While Ash's later actions become all the more suspicious, this moment is the first clue regarding his character arc and twist. That said, it's also a tastefully reserved one, because - as Scott states - a human who had been in cryosleep for that many years would need to move their ts. Therefore, it isn't until the android twist happens that viewers realize that Ash was having some sort of mechanical glitch or test, played off as stretching to mimic the behaviors of humans around him.
How This Improves Alien's Android Plot Twist
Ultimately, this brief scene at the start of the film improves Alien's android plot twist because it's an early nod to the odd behaviors that audiences note in Ash up until his android reveal. Throughout Alien, the crew of the Nostromo are shown to be somewhat standoffish towards Ash, leading the audience to suspect him too. In addition, Ash is shown to make some questionable decisions and know things that other crew do not, which builds his character as the secondary antagonist of Alien. However, while it was clear that there was something sinister about Ash, there was no indication that humanoid robots exist in the Alien universe, with Mother the closest thing to artificial intelligence the film had to offer so far.
Therefore, when Parker knocks Ash's head off, revealing that he is, in fact, an android, audiences are as shocked as the characters on-screen. Where viewers thought Ash was just another regular villain, the Nostromo crew had to face the horrifying reality that one of their crew mates was not human. Therefore, moments that could have been taken as Ash's brief moments of humanity, such as his brisk and slightly off jogging at the start of Alien, are revealed to be setups for the twist.
How Sir Ian Holm Improved Ash
Sir Ian Holm's contribution to the jogging scene shows how much he understood the character of Ash and the direction that story was going to take. It is as though Sir Ian Holm purposefully wanted to throw viewers off Alien's android twist with a clue that could easily be misinterpreted this early on, portraying Ash as though he was just an odd Science Officer hiding something sinister under the surface. It's also a testament to his acting abilities that he could play the nuances of an android trying to fit in as a regular crew member so well.
By having Ash display human-like mannerisms, it became far less obvious that he was an android, even in moments that hinted towards his true nature. His deception makes him even more terrifying, showing how far he was willing to go to protect the Alien Xenomorph, viewing the Nostromo crew as disposable. Ash was just as much of an alien to the crew as the Xenomorph was, making Sir Ian Holm's portrayal of Ash one of the most iconic in the Alien franchise.
