Continuity mistake: When Julia Roberts has thrown all of Brad Pitt's clothes out of the apartment you can see that they change. At first some are in the suitcase and some are on the ground. Then all of them are on the ground. Then back to some in the suitcase. It changes throughout the entire scene.
Factual error: When Gandolfini has the shoot-out with the black assassin, it just doesn't make any sense that the cops who are nearby investigating the "suicide" of Gandolfini's boyfriend don't hear the gunshots and get involved. If the guns had silencers, the whole scene would be more sensible. Come to think of it, the sound-effects used in the shootings sound much like silenced shots but it shows that both weapons are unsilenced.
Continuity mistake: When Jerry is in the Mexican bar, the amount of tequila changes in the bottle and in the shot glass.
Continuity mistake: After Jerry puts the dead guy in his car, the amount of blood on the back of the car seat changes from one angle to the next.
Continuity mistake: At the end of the movie, when Julia Roberts is boarding the plane to leave Mexico, she is the last one to enter the plane and the stewardess begins to close the door behind her. The next shot is of a moping Brad Pitt, but in the reflection of the glass he is standing behind, you can see an open door with people still boarding the same plane.
Continuity mistake: Near the end of the film, Jerry tried to wreck the car. As a semi begins to slide towards them in the El Camino, the passenger door of the semi is open. After the car passes the sliding semi there is a shot from behind of the semi and the door is shut.
Other mistake: In the Mexican after Jerry kills "Leroy" (James Gandolfini) by the car near the end of the movie, he is still breathing. When Sam gets over to the car and starts yelling at Jerry, watch "Leroy" and he is still blatantly breathing. To the best of my knowledge, dead people don't breathe that heavily.
Continuity mistake: When Jerry (Brad Pitt) goes to the bar in Mexico and sees the Mexican for the first time, the guy that's showing him the gun takes him into another room. Then there is a cut to the gun, and then a cut back to Jerry. When this last cut is made, it becomes obvious that Jerry and the owner of the gun are back in the bar room where they started, despite not going back there.
Continuity mistake: When Sam climbs out of the trunk of the car and sits down in a doorway, some of her necklaces are turned backwards. Then when Jerry puts the ring on her finger, they are turned back around.
Continuity mistake: When Brad Pitt is downstairs fighting with Julia Roberts, who is up on the balcony, Brad has on two rings. A pinky ring on his right hand and a ring on his ring finger on his left hand. They start out that way and then at one point in the scene, both rings are on his left hand, and then we see them again shortly after that, while they are still fighting, and they are back on the original fingers on his right and left hands.