minor plot hole: when edwin is first found hanging upside down from his parachute, royce asks him if he has anything to cut himself down with and edwin yells "no, what?!". but very shortly after that when the russian tries to touch a alien plant, edwin takes a scalpel out of his pocket to show the russian the plant is poisonous. no one bothers to wonder why he lied about having an extremely sharp knife. and to make this worse, it makes less sense that a real doctor in plain clothes would be carrying around surgical tools that would be unless sterilized thoroughly before use.
for a movie about a bunch of people from all over the world, it must be a massive coincidence that they all speak fluent english
minor plot hole: once they get to high ground they finally see that they are on an alien planet with 3 other huge planets in the sky and a moon but why didn't they see this during their free fall at the beginning of the film? even during a life or death free fall, i would notice 3 planets that close. but special ops marksmen didn't notice 3 planets? especially if the planet isn't rotating enough to even notice the sun isn't moving. why is it that you only see these massive planets in that one shot? a massive planet should be pretty hard to leave out of the entire rest of the film.
it's also hard to believe that a group of highly trained marksmen/ soldiers would think it's a good idea for all of them to simultaneously empty entire clips at the very first aggressor that they come across. (the alien dog)
minor plot hole: it's well know that in order to activate their cloak, the predators use the wrist mounted control system that seems to be the focus point of their technology entirely. but it is unexplained as to why noland can understand their language enough to turn the cloaking device on and off at will. i have a hard enough time setting up my microwave, let alone using a highly advanced alien device.
major plot hole: speaking of, if you were trying to "stay low" from an advanced alien race that wants to skin you alive, why would you turn on the power of a massive fallen alien ship that is clearly visible? because you totally won't be noticed like that.
why are highly trained soldiers willing to fall asleep around a man that is clearly insane while stuck on an alien planet.... completely letting their guard down? it would take no less than 20 tylenol PM to put me down during all that.
Since all of the other "prey" brought to the planet are obviously highly trained killers or very dangerous people, no one seems to wonder why Edwin (the doctor) was brought to the preserve.
Minor Plot Holes
It's never explained the how the "prey" dropped into the preserve wake up in enough time to slow their descent using the parachute. Or why such a diverse group would include so many who actually know HOW to parachute safely.
Minor Plot Hole
Hanzo, the Japanese gangster, has two entire fingers from his left hand removed. This is incorrect as the yakuza (boryokudan) will only force members to remove the tips of fingers. Mistakes beyond that point are almost always dealt with by killing the offender.
Minor Plot Hole
The AA-12 shotgun carried by Royce (Adrien Brody) is actually only a prototype weapon. It isn't used in combat by any armed force anywhere in the world and it's not particularly useful for anything other than close combat roles. Shotguns have never been primary combat weapons as they lack range, their rate of fire is too slow and their ammunition is too heavy to be easily carried by soldiers in the field.