According to some websites, in Thai when men say Thank you, it should be Kob Khun Krap and when women say it, should be Kob Khun Ka. In this film however, both Cage and Yamnarm's character's use Kob Khun Ka.
During the scene that Joe kills Surat's gang members which was sent to kill him. When Joe goes down from the stairs, he asks the injured gangster about where is Kong. He said in Thai "Yoo Nai Kong". However, in Thai grammar, subject should place before verb. So, he should say "Kong yoo nai" instead.
When Joe and Fon are walking in the park and Joe gets mugged, both the muggers and Joe are behind Fon, yet after she turns around and Joe and Fon have the emotional, wordless exchange one dead mugger is in front of Fon.
When Joe blows Surat's aide by a grenade in the climax scene, we see the body of the man splits in two. Next shot is of the room door exploding due to the grenade blast. Then again we see the man's body splitting in half. The torso flies off over Joe and the limb portion remains in front of him. In the next shot both the torso and limb parts disappear and Joe goes inside the room.
When Joe is sighting the Thai politician through his rifle scope, the reticle changes from a varmint reticle with two horizontal crosshairs and a ladder sight for elevation and windage in the bottom of the picture, to a standard Duplex crosshair with windage and elevation marker lines.
When Joe injects the needle with heroin into the arm of his helper in the beginning of the movie you can see the base of the syringe move, which wouldn't be possible if there was a needle attached to the syringe and in his arm. It's also a rather obviously prosthetic vein he's injecting into - the skin on the helper's arm is wrinkled for a couple of inches ahead of where the needle goes in, and it's also possible to see where the edges of the prosthetic are adhered to the actor's real skin.
When Joe arrives in Bangkok and he shows the customs agent his fake Canadian passport, his name at the top is Cadillac Vincent with two "L"'s, but at the bottom of the passport it is spelled Cadilac Vincent with just one "L".
The goof item below may give away important plot points.
In the first shot of the ending scene where the car is at the gate the police cars are positioned well and completely block the road. No escape seems possible. But in a second shot where the car is rolling slowly backwards there is huge gap between the police cars which could lead the viewer to think that an escape could in fact be successful.