Continuity mistake: When Tuco walks over to the dinner table, just after Angel Eyes finishes saying "It's been a long time," he has his right hand lowered on the table. When the shot cuts, his right hand is raised above the table. (01:38:53)
Continuity mistake: When Tuco sits down at the dinner table, he scoops up a spoonful of stew. There are pieces of spinach hanging off the spoon. Angel Eyes then has a spoonful to prove it is not poisoned, but when the shot cuts back to Tuco, the pieces of spinach hanging off the spoon are no longer visible. (01:39:05)
Continuity mistake: Angel Eyes hands Tuco a bottle for him to drink from. When Tuco is handed the bottle, the label is facing towards him. Angel Eyes then asks him why he is going by the name Bill Carson, and the next shot shows the label facing Angel Eyes. In the shot after that, the label is facing Tuco again. (01:40:35)
Continuity mistake: When Tuco is thrown onto the table by the corporal, Angel Eyes puts his hands on Tuco's shoulders to stop him from landing on him. When the shot cuts, his hands are nowhere near Tuco, and Tuco's position on the table has suddenly changed. (01:45:53)
Continuity mistake: When the corporal stops squeezing Tuco's eyes, he moves his hands away and puts them on Tuco's beard. His right hand appears to be at a straight angle when he does this, but when the shot cuts, his right hand is at a bent angle. (01:46:18)
Continuity mistake: When the soldier at the train station is asking the corporal where Tuco is being taken, there are two men wearing suits behind them who are standing in the sunlight. In the next shot, the two men are suddenly in the shadows. (01:49:43)
Continuity mistake: When Tuco pulls the corporal from train they fall down a steep grade. When train runs over the corporal, they're on flat ground. The corporal would be too heavy for Tuco to carry far enough for the ground to flatten out. Watch the ground when the train approaches before the jump. (01:54:55 - 01:56:07)
Continuity mistake: When the train is about to run over the corporal's body, there is a shot where Tuco braces for impact. In this shot, the corporal's right foot is pointed directly to the right. Then it cuts to a POV shot of the train, and the corporal's right foot is pointed to the right but more at an upward angle. (01:56:25)
Revealing mistake: When Tuco climbs back onto the train after he uses it to cut off his chains, the film appears to have been sped up, as his bodily movements appear unnaturally fast. (01:56:40)
Revealing mistake: After the explosion blows a hole in the wall and Tuco joins the procession of people flowing down the street, when the shot switches to face the characters you can see that the 'woman' in a blue dress in the wagon is actually a man. (Time is for the extended version of the film). (01:59:15)
Continuity mistake: Tuco opens a door to find a bathtub filled with water. When he opens the door, his left hand is positioned a few inches away from the edge of the door frame. But in the next shot, his left hand is directly on the edge of the door frame. (02:00:52)
Continuity mistake: When the bounty hunter bursts into the bedroom while Tuco is taking a bath, Tuco's left arm is above the water. When the shot cuts back to Tuco, his left arm is under the water. (02:02:08)
Continuity mistake: When the bounty hunter falls to the ground after he is shot by Tuco, the doors in front of the bath close behind him. Tuco then stands up to get one last shot, and one of the doors is suddenly open. (02:02:37)
Plot hole: After Blondie has "teamed up" with Angel Eyes, he hears a gunshot and says something like "Every gun sings its own tune", indicating that he's recognized the shot as being from Tuco's gun. But how did Tuco get his gun back? It certainly would have been confiscated when he entered the prison camp, and the chance that the guard on the train has that exact gun is extremely unlikely - he would most likely have had an officially issued sidearm. (02:02:52)
Suggested correction: There's a mistake in the question. It was Blondie who said that quote, not Angel Eyes. The question assumes Blondie was referring to the sound of the gunshots. It's more likely he was referring to the cadence of them. Tuco fired with a particular rhythm that Blondie came to recognise. Considered from this perspective it all makes sense.
Suggested correction: It's the type of gun Tuco likes that makes that particular sound.
Continuity mistake: When the Union general is about to begin walking so that he can show Blondie and Tuco the bridge, he says, "Let's go," and lowers the bottle he is holding. Then it cuts to a wide shot where he starts walking, and the bottle is suddenly raised. (02:14:50)
Continuity mistake: When the Union general shows Blondie and Tuco the bridge, he is holding a bottle in his left and right hand, near the bottom. In the next shot, the bottle is in only his right hand and is held near the top. (02:15:08)
Continuity mistake: Blondie and Tuco carry a box of explosives by placing it on a stretcher and holding opposite sides of it. On Blondie's side of the stretcher, there is one wooden slat that appears to be a small distance away from the rest of the wooden slats. Seconds later, when they reach the bridge, there is no gap between the wooden slats. (02:24:35 - 02:25:13)
Factual error: When Clint Eastwood blows up the bridge, he lights only one fuse but all of the explosives detonate simultaneously, despite being attached to numerous, separate pilings. (02:29:03)
Suggested correction: This is entirely possible. A stick of dynamite exploding will set off a violent shock wave, and any undetonated explosives within ten or fifteen metres will go off. It's called a sympathetic detonation, and when setting explosives, technicians have to be very careful to take it into account.
Continuity mistake: When Blondie and Tuco are planting dynamite to blow up the bridge, they are standing in the water. During the following blast, they are hiding away next to the river and from then on, they are totally dry again. (02:29:05)
Revealing mistake: When Tuco is trying to avoid Blondie firing at him with the cannon, there is a shot of him running while an explosion occurs next to him, followed by another shot of him leaping to the ground and rolling over. In both of these shots, Tuco is replaced with a stunt double. (02:36:06)
