I'm not really saying it's supernatural - but it doesn't really seem totally constrained by the what physically make sense, nor does it seem to have the motivations of an animal trying to survive and procreate. I do think adding those scenes would have changed things, but that's sort of the thing - they chose to remove the scenes that added details on how Alien is an animal that eats, grows, and procreates, and kept the scenes showing the Alien as sadistic, intelligent, and cruel. They made sure we knew that it killed Lambert slowly, but we never get a reason why it's killing (or capturing) anyone at all, other than out of sadism. With the shed skin, it's still just beyond realism for something to grow that much in such a short period of time - whether it eats food or not doesn't really make that big a difference in how plausible it is.

In Alien it just never behaves like an "animal". It doesn't kill to feed or procreate - it kills slowly and sadisticly, seemingly just because it's evil. It doesn't even kill with efficiency, but seems to be taking its time to be cruel. But in Aliens, they have much more grounded behaviour - they capture people so they can procreate, they ambush people to protect their hive. They seem more like grounded biological creatures acting in their own self interest - Ripley is even able to communicate with the Queen that she is threatening its eggs, and negotiate a safe exit. In Alien, it's entirely a monster, that seems to exist entirely to be a dark twist on humanity that cruelly murders people. Note that when Ash "admires its purity", he specifically talks about its lack of morality, rather than its physical strengths.

Given that its behaviour doesn't make sense for an animal, and honestly that it's never made any biological sense, either physically or as a sensible survival mechanism - how fast it grows, having that strong an acid for blood, how long the facehuggers attach for, having no eyes, how slow it is at ambushing, that in Alien there's seemingly no reason for why it kills things etc - I think it just is a thing beyond our understanding that doesn't need to make physical sense. It's not literally some spiritual "demon from hell" of course but it's definitely more than just "scary animal", and I think that also fits in with the themes of Giger's art.

Yeah, it kinda comes down to how you think about Alien and Aliens and how you approach the different visions the directors have. You could see Alien and Aliens as really describing the xenomorphs quite differently - that Aliens is kind of a retcon that changes the implications from Alien. But you can also try to reconcile them - pretend that the Alien universe is actually real, and not just made up by writers and film crews - then there's enough ambiguity that you can interpret Alien as a narrow glimpse into a universe that we see more of later.

It's just something I noticed recently when watching Alien and Aliens back to back. I've always loved Aliens and it was my favourite movie out of the whole franchise. But I'm now able to see that there's something different about Alien that none of the other movies have captured - there's something truly evil about the xenomorph, in how human it looks and moves and behaves, in how it's designed with twisted forms of sexual imagery - whereas in Aliens, they're almost just cool-looking predators that are good at fighting. It's not necessarily about the canon really being contradicted - but there's definitely a different vibe after Alien, especially when you get stuff like crossovers where Green Lantern fights the xenomorphs. It's still very cool, and honestly it's part of why I grew up loving the franchise and pretending to be a space marine, but as an adult, I can now see how Alien does stand out a bit compared to the rest of the franchise.

In Aliens, where they are depicted more like biological creatures, sure. But in Alien, it's almost portrayed as some sort of sadistic evil demon thing, a twisted dark reflection of a human, and I wouldn't expect it to obey the laws of physics necessarily. It's kinda low how they don't have eyes.