When Dutch is running from the Predator, and trying to lead the beast into the small tunnel which contains the "trap", a quick cut-away shot of the trap mechanism appears to be a photo of the trap, as opposed to "live" footage, and even appears to be a bit out of focus.
During the attack on the guerrilla camp, Poncho and Hawkins enter the main palapa and kill a couple of soldiers immediately. As one of the soldiers is falling, he discharges his weapon several times, but no sound is heard.
When Dillon is requesting extraction over the radio, he says, "Blazer one, I repeat, extraction necessary." The word repeat is never used in that context in the U.S. Military. Instead of "repeat", "say again" is used. Dillon actually gets it right in his next sentence, "Say again Blazer one, say again."
The mini gun that Blaine wears fires over 6,000 rounds per minute. Blaine easily fired over 6,000 rounds, and not only are there no shell casings, he could not carry that much ammunition, as it would weigh well over 100 pounds and there is not nearly enough room in the ammunition pack on his back.
Billy has a M16 with a shotgun attached to it. In the scene right after they leave the rebel camp you can see Billy with a "normal" M16 without an attached shotgun. One moment later he has his own rifle back again...
Right after Dutch gives the plan for attacking the rebel camp, Blaine and Mac walk off screen to the left. Blaine is carrying the mini-gun ready to use it. In the next shot the mini-gun is shouldered and his M16 is being carried.
During the terrorist camp attack, a man with a mustache, red bandanna on his neck and a hat is seen shooting down at Mac, who promptly hides behind some rock and tells Blaine to help and kill him for him. Blaine fires ahead and the man is then seen being shot dead, falling down and smashing through a roof next Hawkins and Poncho. Next, some more terrorists are seen to pop up to start shooting, one of them being the same man with the mustache, red bandanna around the neck and a hat who was seen being killed just seconds earlier.
When Billy climbs up to discover Hopper and his team's bodies he is wearing nomex flight gloves. A moment later he is shown barehanded as he shields his face from the buzzards, only to be wearing them again as he emerges from the brush.
When Dutch is being pursued by the Predator and is sliding down the hill that leads to the cliffs, there is a rocky and dry riverbank extending at least 50 or more feet from the cliff base, to include a tree between where Dutch would land and the river. In the next shot, Dutch falls into to a deep body of water with no riverbank at the cliff's base.
When Dutch catches the dog tags of Lt. Hopper, they hang off the side of his hand. In the following shot (from Dutch's point of view) they are sitting nicely in his palm. It then cuts back to the full body shot of Dutch and they are hanging off the side of his hand again.
Near the end when Dutch is alone and waits for the predators arrival after setting up his traps, it's late at night. However in a cutaway shot showing the predator leaping down from the trees shortly after-wards, its in the middle of the day. When the camera goes back to Dutch with the predator behind him, it's night again.
Dutch lights an explosive and tosses it at the Predator. When it explodes, Dutch runs and jumps on a branch. In the first shot with the branch, it has a curved end. When Dutch grabs onto the branch in the next shot the branch has no curved end.
When the team sets up the tree trap, Dillon is seen in the background of one shot shirtless and helping out; in the next instance, he has his shirt on and is told by Dutch "Instead of complaining, maybe you should help".
At the beginning of the movie when Dutch asks Dillon who their reinforcements are you can clearly see Poncho sitting next to Dillon, but Poncho doesn't move next to Dillon until later when he tells Blaine to strap the grenade launcher on his sore ass.
The length of Dutch's cigar changes drastically during the Jeep ride from the helicopter. Dutch is seen lighting the new Churchill sized cigar when the chopper lands, but when he walks up to the General, it is several inches shorter. That type of cigar takes a few hours to smoke, so the Jeep ride across the beach would have to be about 45 minutes long. Additionally, his cigar is shown to be even shorter in the next scene inside the General's HQ.
After Dutch swims to shore, he falls on the left side of his face. When he turns around to look at the Predator, we can see that the right side of his face is clean. A little later, after Dutch struggles into the brambles and turns around, his entire face is covered in mud.
When Arnold is swinging through the trees trying to get the predator to follow him into the trap, there is a clip where he his hugging the tree and his hair is messy. There is a pan of the forest then back to Arnold but now his hair is all neat and tidy.
When the team is attacking the terrorist camp and Dutch launches a grenade from his attached M203 grenade launcher, there is an explosion that sends a terrorist flying in the air. Few seconds later Poncho uses his grenade launcher to attack the camp, but the same explosion with the same terrorist is shown once again.
(at around 20 mins) When Dutch takes the binoculars and slides down the hill, a vine gets caught on the right side of his gun belt. He drags the vine most of the way down, and when he reaches bottom you can see the vine hooked over the butt of his sidearm.
In the pan-and-scan version, when Billy first finds the bodies of the skinned green berets, he is startled by the vultures as they fly away. In a quick overhead shot, a camera can clearly be seen below him.
Anna sneaks up behind Dutch with a gun. Dutch then hits Anna on the side of the head with his gun. If you look in the lower left corner of the screen, right when Anna is about to fall, you can see someone's hand touch Anna's back to help her "fall" to the ground. (Non-widescreen version only).
It is not possible to fire a mini gun, which Blain carries, without some power source, which he does not carry; the pack on his back only contains ammunition. Further more, if a human were to fire a mini gun with live ammunition, one would be propelled backwards by the recoil.
After the mortally wounded Predator activates it's self destruct device he begins laughing hysterically with Billy's laugh which it had recorded earlier. However the Predator's sound mimicry is presumably a function of it's helmet which means it shouldn't have been able to do this since the Predator removed it's helmet at the beginning of the final battle with Dutch.
During several scenes in the movie, permanent blank adapters can be seen in the muzzles of the various weapons carried by Dutch and his team. Most notably, the scene where Mac is walking through the bush with his M60 barrel pointed towards the camera, and another scene where Billy is shown emerging from the bush with the muzzle of his M16 pointed towards the camera. There should only be one hole at the end of the barrels of each weapon, but what can be seen is a small reversed cone shape inside the flash suppressor indicating permanently modified blank firing weapons.
After Anne runs away from Dillon and is caught, Dillon lifts her up and her hands are in front of her "bound" together. One of the zipties that is supposed to be around her wrist is hanging loose and her hands are clearly no longer bound, although she holds them together as if they were.
When Mac fires into the trees with the mini-gun it cuts to a quick wide shot behind him showing some of the trees in front falling down. However if you look carefully there's some trees that are being "shot down" and falling over before Mac has even fired in their direction.
In the early scenes when Dutch's crew attacks the enemy camp and specifically just prior to engaging the helicopter, the pilot jumps into the helicopter and tries to shut the door. The door begins to fall off the helicopter revealing that it is only a flimsy set piece rather than a real helicopter.
When Anna Poncho with the log you can easily tell it's made out of a foam material, because after making contact not only does it easily break and crumble in a awkward fashion but also no sound is produced from the impact.
When Mac is firing the mini-gun into the jungle and the camera pans down the line of all of the soldiers firing, it is obvious that the belt fed ammo at the right of the mini-gun is not moving, nor are any shells being ejected.
As Dillon and Anna walk by Mac after the fight at the compound, a supposedly dead soldier can be see rolling his leg around. He's the one lying directly next to the barrel, and can only be seen before Mac takes the scorpion off of Dillon's back.
When attacking the terrorist camp Dutch goes to the truck used a power source with a belt attached to the rear wheel. When Dutch cuts the belt the truck is in reverse gear, when he lifts it and pushes into the compound you can see the the truck is now in a forward gear without Dutch entering the cab and changing gears.
When the crew encounters the helicopter which crashed while bringing the first team of operators sent in a week earlier, it is clear that not only had this helicopter not crashed, it hadn't flown in many years (rust is visible, and parts have clearly been removed, etc)
The goof items below may give away important plot points.
When they first hit the guerrilla village, after the initial explosions and gunfire, but before they actually assault, Dillon is heard saying, "Target's the center of the palapa," yet his mouth is not moving.
After Mac's head is obviously blown to pieces by the Predator, Dillon catches a glimpse of his dead body with his head intact. Additionally, when we see Mac's cleaned skull, it has a surprisingly neat entry wound for something hit by a plasma-based energy weapon that can destroy trees. Also, there's no visible exit wound on the skull, despite the earlier depiction suggesting that there was a fairly explosive exit.
The fatal shot to Blaine's chest fits inside his shirt's MTV logo, roughly a six to eight inch circular wound in the center of his chest. After the shooting spree, when the team looks him over, the wound is dramatically larger; now the entire front of his torso is blown open, nearly a two foot gaping hole.
After the scene where the whole team embarks on a shooting spree into the jungle (after Blain's death), Dillon gets on the radio to ask for help "Blazer one I repeat extraction necessary, say again blazer one, say again!" The first shot shows Dillon facing in Anna and Poncho's direction. When the camera zooms in for the next shot, Dillon is facing away from Anna and Poncho.
In the final battle scene, before the Predator takes off his mask, Dutch can be seen leaning back against a tree; from the Predator's view, he is standing in the clearing, hunched over in a ready position.
Almost at the end of the movie (everyone but Dutch has died), when Dutch is walking (semi-crouched) through the jungle with his assault gun, it can be clearly seen that the leaves in front of Dutch are being moved by the camera going backwards in order to follow Dutch.
(at around 1h 08 mins) When the Predator is walking away right after he had blown Mac's head, in the next shot you can see Mac's body going into death convulsions . In the upper side of the screen, right below the highest tree branch, the camera (from which the view of Mac's head blown was shown) is clearly being pulled up by the cameraman.
The snake that Dutch sees when he is looking for the body of Hawkins is a Burmese python. The only large constricting snake in central America is the Boa constrictor which isn't as big as a Burmese python. Since the movie was filmed in Mexico the question becomes, why didn't they use a Boa? Burmese pythons are indigenous to southeast Asia.
When Dutch is being pursued by the predator, he hides from its infra-red vision using mud. While freshly and thickly applied mud would help minimise his heat signature, it would not take the body long to warm the mud to a higher temperature than the surrounding vegetation; especially the thin and inconsistent layer we see Dutch covered with. He certainly would not be invisible, just somewhat less obvious.
The last scene of the movie, where the helicopter is flying out of the jungle, the aircraft has it's anti-collision lights on. This is standard for peacetime operations, but no military pilot would fly in a "hot" territory with them turned on, as they are designed specifically to draw attention to the exact location of the aircraft.
The Predator uses two large retractable blades, each probably close to 20 inches long and 4 inches wide, to kill Major George Dillon. The Predator stabs Dillon in the abdomen with enough force to actually lift him a foot or so off the ground. With the length of the blades and the location in which Dillon was stabbed, he certainly would have not been able to scream as long and as loud as he did. There simply would have been too much internal damage done by these large blades. Given their length and the fact that they did not exit his back, the blades would have had to go up, thus piercing his diaphragm and one or both of his lungs. Dillon could have, at best, only managed a gasp.
In the original uncut version, when Major George Dillon has his right arm shot off, the camera pans around his back and you can see his right hand poking out under his shirt, in the next shot his hand is not there.
When Billy is about to have his spine removed by the Predator, you can clearly see him closing his eyes before hitting the log and then quickly reopen them after impact, even though he is supposed to be dead.
The looped cord for the rigged booby trap (seen going up when Dutch trips it) is a matte added in, partially transparent. Additionally, when Dutch is constructing the trap, this rope, the one that would have pulled the Predator's head or next up and into the stakes, was actually several vines, whereas the rope added later was only one strand.