Other mistake: In the very last scene of the movie, and just before Blondie shoots the rope that is holding Tuco on the grave's cross. You can see a car moving in the background, screen right of Tuco's head. (02:55:29)
Suggested correction: I've just watched this scene; there's no car visible. There's a bit where Blondie prepares his gun prior to aiming, then the camera switches back to Tuco. To the right of Tuco, in the background, a blurry something can be seen for maybe a second moving right to left. The object is far too blurry to identify. There's no reason to believe it's a car. It makes more sense that it's a horse-drawn wagon.
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.
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.
