The Professionals (1966)

Deliberate mistake: When Raza is chasing the "empty" train, as it goes over the trestle just before he stops it, you can see the engineer in the train's engine.

Factual error: In the scene where Lee Marvin states that Burt Lancaster loves explosions, Burt Lancaster makes a remark about the big bang theory. He says: the whole universe started with a big explosion. The film is set in 1917 which is 10 years before Georges Lemaître launched the big bang theory.

Continuity mistake: When rescuing Burt Lancaster whilst tied upside down in the canyon, watch the two bandits behind Lee Marvin when he jumps down, as they retrieve the rifles stood up against the rocks twice.

J.W. Grant: You bastard.
Rico: Yes sir. In my case an accident of birth. But you, you're a self-made man.

Bill Dolworth: The revolution? When the shooting stops, and the dead are buried, and the politicians take over, it all adds up to one thing: a lost cause.

Jesus Raza: You know, of course, one of us must die.
Bill Dolworth: Maybe both of us.
Jesus Raza: To die for money... is foolish.
Bill Dolworth: To die for a woman is more foolish. Any woman. Even her.

Question: Who was the $10,000 for?