When the Predator regains consciousness at the slaughter house resuming his chase after Harrigan, he sees Harrigan in infrared scope, a major bloop, as the Predator didn't put his mask back on. Anyone who watched the 1st installment must remember: without the mask the Predator can only see in red, with only minor distinctions (i.e. hand-to-hand combat with Schwarzenegger). The Predator didn't put his mask back on all throughout till the very end, occasionally using his respirator seen on the rooftop sequence etc. Inside the Predator's spaceship, again, he sees Harrigan down on the floor in infrared.

In the opening sequence, Harrigan chases one of the Columbian drug dealers up to the roof of a building. The Columbian fires numerous rounds before falling off the building, and shell casings are scattered over the roof. Harrigan climbs up and looks over the side of the building, and the shell casings are all gone. After looking over the roof, the shell casings are back.

During the sequence where the special forces team is attempting to trap the alien, several shots were edited to go back and forth between the team and the ops center. When we first see the monitors, a little over two minutes has been recorded. When next we see one of the monitors, it show's only about one and a half minutes have elapsed.

During the opening credits, a radio voice is heard saying the temperature is 109°. As the camera moves in on the city, the buildings are shown dark and a few windows are red, indicating they're significantly hotter than 109. As it moves to the scene of the gun battle, human figures are also shown in red. But even when active, a human's core body temperature remains around 99°, and skin temperature is a few degrees lower. So with the air, ground, & buildings at 109, the humans should have appeared as dark silhouettes.

When the Colombians are rearming themselves after getting back into their armory, one if them is shown placing a round on the bolt of the Iver Johnson AMAC-1500 rifle, then shortly later, it shows him pulling the bolt from the gun. These 2 scenes are obviously reversed, as the bolt has to be removed in order to place the round onto the bolt.

When Lt Harrigan is engaging the Predator in the meat locker, and the Predator's mask is removed, the view from the Predator is still as if the mask is on and using an infrared view when in fact, as seen in the original Predator, should be a poor level of vision, in a blurry red and grayscale view by the Predator.

The drug lord that falls from the roof of the building, after Harrigan shoots him, lands on a table. Considering his size and the length of the fall, the table would most definitely have been crushed or collapsed.

After the subway incident the EMT examining Leona is listening to her chest. He says "I can hear fetal heart tones. This woman is pregnant." Never mind the significant level of background noise, there is no way that he would hear any fetal heart sounds with a conventional stethoscope while listening to the chest.

The periodic table of elements is a sequential list, and it has no gaps for "unknown" elements. Every position from 1 (Hydrogen) to 118 (Oganesson) is known. The only elements that aren't on it are so heavy that they don't yet exist, and they'd be dangerously unstable & radioactive.

During the slaughter house scene, Peter Keyes (Gary Busey) is sliced in half with the Predator disc weapon. The upper part of his body seemingly stays up in the air while the lower part (legs etc.) slumps to the ground.

The Predator is shown walking with King Willie's decapitated head and King Willie is screaming. Decapitated heads cannot speak or make any other vocal noise since the lungs moving air over the vocal cords is required to vocalize. However, the scream is supposed to be from their earlier fight, and is merely overlaid for dramatic effect.

When Harrigan and crew consult with the medical examiner about Danny's and the gang member's killings in the condo there is an interesting error. Harrigan shares with the doctor the spear head he found in Danny's hand. Noticing its near weightlessness, she immediately places it in an electron microscope. Simultaneously, an atomic analysis of the spear head determines it is made of an unknown material not on the periodic scale. An electron microscope could "look" at the surface structure of an item but not analyze and determine the actual metallurgical composition of the metal. This would have required an entirely different instrument such as a GC-MS and would have required a lot more sample preparation. Actually, Electron microscopes can be equipped with an EDX detector capable of element determination.

When Harrigan fights the Predator on the rooftop, the Predator activates his wrist bomb which Harrigan stops from blowing up by cutting off the Predator's hand. Surely, the Predator's wrist bomb would have still detonated when Harrigan cut off the Predator's hand. In "Alien Vs. Predator", when the Predator activated his wrist bomb and removed it, the wrist bomb detonated and blew up the pyramid.

Harrigan didn't just cut off the Predator's hand, he also cut through the bomb device itself, which effectively disarmed the bomb. In the overhead shot of the predator falling, sparks are seen bursting from the bomb segment which has remained strapped upon the severed hand.

When Danny climbs the pillar to retrieve the spear tip in the ventilation duct, he is crawling on his knees and then rises up while still on his knees. Once he retrieves and looks at the spear tip and is startled by the Predator's voice, he is shown to be losing his balance on his feet, trying to get his footing. At no point did Danny actually stand up...he cannot lose his footing because he was still on his knees.

Lt. Harrigan tells the scientist that he pried the "spear or harpoon tip" from Danny's hand. But Danny clearly drops the object (you can hear it impacting the ground) when the Predator encounters him near the A/C unit.

When Keyes is cut in half, his body is partially hidden behind slabs of beef. His legs fall to the floor along with a large amount of blood, but his torso never falls.

Cable visibly attached to the actor in one shot when the Predator falls down the side of the building.

As the Jamaicans assault the penthouse, you can see one of the people that is supposed to be dead, move his foot out of the way as the men move by.

When the Jamaican stabs the hanging Colombian to remove his heart you can clearly see the blade retracting into the handle.

The Predator's telescoping pike is actually two special effects props, depicting a first and second stage elongation. In the scene where The Predator deploys the pike on the slaughterhouse rooftop, you can see him drop the first stage pike prop out of frame before the camera zooms in on him and he grabs the fully extended pike prop.

Towards the end of the film, when Lt Harrigan is in the Predator space ship, he sees the various "trophies" on the wall, one of which is an "Alien skull" (xenomorph), as if a human based skull (white bone), when in fact Aliens are/were a species that utilized an exoskeleton, much like insects, having no bones, but an armor like exterior that was grey/silver/Black.

The "Chief Pathologist for the City" of Los Angeles remarks about the spear tip that Mike (Lt. Harrigan) brought to her that "none of these elements appear on the periodic table," and as such, she would have instantly recognized the spear tip as not from earth and would have pressed Mike incessantly to keep it, since the Lieutenant had no further use for it.

When testing the alien spear tip, the female doctor says that they are viewing the image at 150,000 times normal magnification. However, when the camera cuts back to the doctor at the point at which she says "magnification", her lips aren't moving.

When Harrigan's crew first enter the penthouse and Lambert runs into the hanging body there is a crewmen in the shadows along the right side of the screen just visible under the body manipulating something with his hand.

When Harrigan is chasing the predator after the subway incident, the predator climbs up a building and Harrigan takes a nearby car and you can see the shadow of the camera on the street.

When El Scorpio fires the grenade launcher towards the 2 shielded swat members and the police car explodes behind them, you can clearly see the cable pooling the police car to make the exploding flip.

The movie takes place in Los Angeles, but when the characters get on the subway, suddenly they are on San Francisco's BART system, not LA's Metro Transit Authority, which consists of light rail trains. You can see during a shot of the front of the train that it has a distinctive BA, the first two letters of BART standing for Bay Area, instead of the MTA printed on the side of the cars in other shots.

The human body needs to constantly radiate a certain amount of heat or it will overheat and the person would eventually die. Therefore, there is no such thing as an "infrared insulating suit", as it would be necessary to transmit this excess heat to the outside of the suit. This makes it impossible for humans to be invisible to the Predator's infrared vision.

Keyes' forensic team sweeps the gang leader's penthouse, yet somehow they completely miss the "spearhead" that Danny had spotted with his naked eyes. It is left there for him to try to retrieve later in the evening. Surely such an obsessive government cleanup team would be more observant than that.

@ around 2 minutes when the guy finishes his interview with KNLB 10 upon hearing mass gunfire a boom mic can be seen briefly dropping in to frame (top of screen in the centre)

When the alien artifact is under the electron microscope the tech says magnification is now at 150,000 times, but the monitor shows 14,250X.

During the scene when the special forces team is getting slaughtered in the meat-house, Harrigan is suiting up and loads his M16/M203 weapon. He pulls the charging handle (to load the magazine), the scene then cuts to an indoor shot of the predator stalking the team. When the scene comes back to Harrigan, he pulls the charging handle to once again load the M16. There is no need to do this twice.

In the opening scenes, a banner on the screen identifies a news report as originating from "KCMQ Cable News". KCMQ is a broadcast designation, not a cable designation, which is not restricted to the three- or four-letter format beginning with "K" or "W". WTBS dropped its "W", leaving WGN as the only cable/satellite network to retain its regional designation.

In the beginning when the two officers and the big guy start a brawl, third officer who comes to help, keeps smiling.