In the beginning scene when the Expendables are raiding the enemy territory and about to crash through a building, Gunner yells to Yin Yang "Watch your head, insect!", but if you watch his mouth movements, he was clearly saying something else at the time which was dubbed over with the new line.
After the airport fight, Vilain and some of his men are seen arriving at the hangar on a lifted truck with a regular V8 engine sound. It's actually a Toyota Hilux and the 3.0 D-4D badge on the door means it's the 4 Cylinder, 3 Liter Turbo Diesel engine which sounds totally different.
During numerous shots, the plane has a rear access door (they load, and then throw out Jet Skis) but in other shots the rear of the plane clearly has no door, the latter being correct as this plane is a Canadair CL-215 which has no rear access.
After the bar scene at the beginning of the movie, Barney is seen riding off on his motorcycle. The license plate of his motorcycle is showing on the left side of the rear wheel in the first shot and then on the right side in the next shot to be shown on the left side again upon arrival at this destination.
When Vilain has a gun at one of the Expendable's head, just after they find the box, you can clearly see he is holding the gun with his right hand. The close up reveals he is holding it with his left hand as his left finger is on the trigger, then the next shot shows him holding it in his right hand again.
After the big fight at the airport, Booker, Church, Maggie and Trench are seen getting in a helicopter with a large 711 on the engine cowling. However, the helicopter we see taking off with them supposedly on board has a large 712 on the engine cowling.
During the airport battle there is one quick shot of Hail Caeser using his automatic shotgun he gave to Trench in the beginning of the movie, and then in the next shot of Trench he's using the same gun. Finally, when it shows Caeser again he's only got his regular pump action shotgun.
In the opening action scene, Barney's mustache stretches all the way down to his jawline when he is driving, then changes mid-scene to the shorter handlebar mustache that he sports for the rest of the film.
As Billy's chest is cut by the double bladed knife towards the beginning and 2 lines of blood are on his chest from the cut, during the scene as they flash to Billy kneeling, the blood disappears and re-appears throughout the scene.
Plutonium is about 20 times heavier than water, so the Plutonium bricks would weigh about 100 kilograms each. It would be impossible for one person to move that much weight as is displayed in the movie.
The guys are seen zip-lining down on a high voltage power line. This could never be possible, as on every pylon, the wire is anchored to an insulator. Even considering the fact that the power was turned off, they could have only zip-lined between two pylons.
The coordinates that show up in the binoculars; N39°93'19" E17°70'56" are not real coordinates, as the minutes (the second number) must be between 0 and 59. During the scenes the coordinates do change, even into an existing location, but that does not represent what he sees through the binoculars, but is in fact somewhere in the Ionic Sea, off the coast from Italy.
As the plane crashes into the mine, people and equipment are thrown to the back as well as debris from the tail. Actually, as the plane is reducing speed during the crash, unsecured people and equipment should have been thrown towards the cockpit. Only pieces that hit the mine's surfaces should be left behind.
In the opening sequence, The Expendables escape by climbing an electricity pylon (transmission tower) and zip wiring along the cables which are clearly shown to be live as indicated by sparks. On the DVD/Blu Ray Director's Commentary, Simon West states that making contact with live cables without electrocution is possible as long as the person is grounded, when in fact the opposite is true. So in reality they would've been electrocuted as soon as they attempted the transfer from the grounded pylon to the live cables. Ironically, zip wiring along live cables also featured in the Stallone film Tango & Cash, but in that movie it was explained correctly that non-grounding prevents electrocution.
After the big fight at the airport, Booker, Church, Maggie and Trench are seen leaving in the helicopter. As the camera pans out on Barney, as viewed from the chopper, there is no wind gust at all and Barney's hair doesn't move from the vortex wind that would be created by the helicopter. Also in this situation you wouldn't be able to look at the chopper directly due to the wind vortex blowing in your eyes.
When the Expendables come across the wrecked aircraft, it is obvious that it is there due to having crashed. The engines are missing, which would be likely in a real crash, however it is obvious that the engine was removed by unbolting it, and not by crash forces. This is evident from the intact bolts and hoses shown forward of the engine firewall.