The events of Prometheus provide a plausible explanation for why Mother was able to decode some of the distress signal in Alien.
A lot of the things that don't make sense about the Xenomorph make a lot of sense if you consider the possibility that they were designed as weapons- Hollywood Acid for blood: defense mechanism as well as the 'living battery' idea proposed in the comics. Ability to reproduce with almost any species: A perfect way of making more of them that demoralizes the enemy in the process, as well as incorporating the abilities of other species in the Xenomorph's 'design'. Taking on the characteristics of the animal they hatch from is even more sensible: that creature was already adapted to its environment, so the Xenomorph is adapted to it, as well, and adding its own advantages. And odds are the Xenomorph is taking as hosts the dominant lifeform in a given ecosystem (i.e., humans for most of the franchise), making it that much more capable.
Might seem horrific, but a lot of Weyland-Yutani's actions are a lot more understandable if you look at it the right way. They want the aliens as bio-weapons. Seems like a fairly typical power-hunger thing that any bunch of General Rippers would do, right? Until you think about who they might need to use them on. The galaxy has just been proven to contain other intelligent, spacefaring lifeforms, or at least it did, ones vastly superior to humanity. And they're probably still around. Even if they're not, other species probably are — indeed, given the implied shared verse, the Yautja are certainly still around. Controlling the aliens provides Earth with a guaranteed-effective weapon against any aggressors. In essence, they're looking for a trump card to ensure the survival of the human race. In that context, they might still be crazy, but they're more Knight Templar types than the omnicidal maniacs that they look like otherwise.
Even moreso, if you consider what Prometheus reveals about the Xenomorph's derivation from Engineer science gone wrong. Studying them doesn't just provide a weapon proven to have taken out Engineer vessels at least twice in the past, but also potential insight into the threat posed by the Engineers themselves.
Robots are difficult to build and expensive AF in the Alien Franchise... If Prometheus is canon, robots were already a thing some 30 years before the first Alien film. But David seems to be a novelty and works as some sort of personal assistant for millionaire Peter Weyland. Then, in Alien, Ash doesn't come across as a more advanced robot than David. Moreover, how come humans are still necessary to man the Nostromo ship instead of just putting there a couple of robots to run the whole operation? If Ash can pass for a science officer, why not some other robot(s) as a navigator or ship engineer? Then in Aliens, again only Bishop is a robot. I can sort of understand that robots may not be trusted to function as colonial marines, but why isn't there any mention of robots as colonists? Instead of sending dozens of humans to colonize, why not send a handful of robots as an avantgarde? Centuries later, in Resurrection, Call is again the only robot in the film, not only that, but the models seem to be getting worse and worse, since by now they question orders. But the real people don't even seem to keep any Ash, David or Bishop models (Bishop being so far the only seemingly trust-worthy model in the entire franchise universe). This implies that the field of robotics is more difficult than thought, and also that robots are super-expensive despite decades of progress between the films, so much so, that they still haven't really replaced humans in menial/dangerous jobs.
There’s something about the oddly-human mouth of the Xenomorph that’s very troubling. That “something” probably being its usual expression before it strikes: it looks angry. Let that sink in a little. Not only does this monster want to kill you/use you for breeding stock, it absolutely fucking hates you.
