Hanging the prey upside down may, according to a Predator, prevent the spirit from ascending, trapping it inside the body, making the kill more valuable. Skinning the victim could signify that the prey is rendered "naked" and defenseless. Some human cultures have the tradition of marking a novice hunter with the blood of his or her first kill. Another possibility that has been suggested is that the skinning and hanging of their victims is a religious or hunting ritual. In other words, the Predator is taunting its prey, as it is stated in the movie, "to scare the shit out of its enemies" like the Jamaicans do. Another theory that's been suggested is that the skinned bodies were deliberately left hanging as a warning to other humans in the area, either taunting them or letting them know that they are also being hunted. It was also established in Predator that the Predator removes body parts, e.g., skulls, spines, and hearts, as trophies, but then again, human hunters taxidermize the heads of their animal prey and hang them on their walls as trophies even if they have eaten the meat. However, the Predator in this movie goes to an abattoir (slaughterhouse) to feed on beef, so it's unlikely that it is also feeding on humans, although it's possible that maybe it takes so long for human meat to cure that the Predator would have gone hungry while waiting, so he was saving the human meat for later. Game animals are also sometimes left hanging for days or weeks in order to season the meat before consuming it. It was established in Predator that the Predator is a "hunter", and hunters will often gut and dress their prey while still in the field. The Predator's reasons for skinning its victims and hanging them is not explained in this movie nor in the first movie. It's also important to note that these are fictional creatures from a science fiction universe and don't have to obey certain real world rules. Since both franchises originated in film format that this film has a skull, it is canon that xenomorphs have a skull.
The comics, novels, and video games have differed on the subject according to the writer and story needs.
Predator) so it's logical that a xenomorph coming from a creature with an endoskeleton would have one as well. a quadruped from the dog/ox in Alien 3, mandibles from the Predator in Alien vs.
Throughout the series the aliens do take on traits of their hosts (i.e. It should be noted that the xenomorph in the original Alien does have a human skull inside its head, while the Predalien from AVPR: Aliens vs Predator - Requiem has a Predator skull. They have been described as bugs by those who are unable to fully study them. At the time this film was made, only Alien and Aliens had been released, neither of which had gone deep into the exact biology of the creatures. The long in-universe answer is that they are not true bugs as we know them. Both science fiction franchises were owned by 20th Century Fox, now part of The Walt Disney Company, while Stan Winston had worked on creature designs for Aliens and Predator. The short real world answer is this was simply an Easter egg for eagle-eyed fans. Some fans have wondered how the Predators could have a skull from a species that has been described a bugs, which in reality have an exoskeleton not an endoskeleton like humans. In the Predator ship's trophy room, there is a skull for a xenomorph from the Alien franchise.