There is no shortage of insanely violent Xenomorph kills throughout the Alien film franchise, but one stands above the rest as easily the most shocking–though apparently, not the most original.
In the fourth installment of the Alien movie franchise, 1997’s Alien Resurrection, the series takes a drastic new direction in the established Alien canon. Set two-hundred years after the events of Aliens and Alien 3–as well as after the death of the series’ protagonist, Ellen Ripley–Alien Resurrection introduces the idea of cloning, both humans and Xenomorphs, through the genetic samples of the last known human to actually carry a Xenomorph embryo: Ellen Ripley herself. In Alien 3, Ripley was incubated with a Xenomorph before she threw herself and the unborn alien into a vat of molten material, killing them both. However, two-hundred years later, these scientists were able to recover fragments of Ripley’s DNA, and through those fragments they cloned not only Ripley, but the Xenomorph she was impregnated with. This allowed the scientists to create a Xenomorph horde–Xenomorphs that they kept in isolated cells that sometimes contained more than one creature at a time. In an effort to escape and claim the ship as their own, two Xenomorphs within a single cage of three decided to turn on the third and kill it, thus spilling its blood all over the cell’s floor and burning a hole through the ground with its acid blood–allowing the Xenomorphs to escape.
In 1989’s Aliens Vol. 2 #1 by Mark Verheiden and Denis Beauvais, Newt and Hicks are in a spaceship traveling away from Earth after the Xenomorphs effectively took over the planet. While they believed they were safe, Newt becomes convinced that there are Xenomorphs on board, so she and Hicks decide to go investigate. As it turns out, this spaceship–which they stole from the military to make a quick escape–was actually transporting Xenomorphs to a scientific lab in the outer rim of the solar system. However, it seems the Xenomorphs got restless in their captivity and decided to make efforts to escape. When looking for the Xenomorphs, Hicks and Newt stumble upon the holding dock where they find one Xenomorph torn to shreds, and places around the ship with holes burned through them–holes the size of a Xenomorph. As Hicks describes when he sees the carnage associated with their escape, “The others must have cannibalized it for the blood”.
It has become established that Xenomorphs are more-or-less a hive mind with the understanding that the needs of the hive are vastly more important than the needs of a single organism. This leads to the Xenomorphs being able to work together so proficiently as they are willing to sacrifice their lives to ensure the continuation of their species, whether that means putting themselves in danger to protect the Queen or being killed by their own kind for the survival of the majority. It is easier to accept that a horde of Xenomorphs will commit acts of horrific violence against a member of another species for their own continued survival than to see them turn on each other to reach the same end, but evidently to a Xenomorph, there is no difference between the two.
When the Xenomorphs turned on each other in Alien Resurrection, it was the first time they had done so in the films, and it was a shocking display of ruthless intelligence the likes of which fans hadn’t yet seen. While it was a smart tactic, it was still incredibly dark, and the act becomes even darker when considering that wasn’t the first time the Xenomorphs had done this as Alien's darkest Xenomorph kill happened way before fans thought.