Deliberate mistake: During Alejandro and Elena's duel, he slashes her skirt and exposes her bare leg. When he slashes off her whole gown, she's somehow wearing leggings. Obviously so Catherine Zeta-Jones would not be naked. (01:38:13 - 01:39:20)
The Mask of Zorro (1998)
1 deliberate mistake - chronological order
Directed by: Martin Campbell
Starring: Anthony Hopkins, Antonio Banderas, Catherine Zeta-Jones
Continuity mistake: When Alejandro and Captain Love are fighting on the gold lift, Alejandro punches the sword out of Captain Love's hand. He grabs it and stabs it through him. When it shows the top view of the sword stuck in Captain Love, hit the pause button. Look at the sword blade going through Captain Love's stomach.Then look at the other end of the blade going out of his back. They are at different places in him. (02:03:00)
[Alejandro draws his sword.]
Don Diego de la Vega: Do you know how to use that thing?
Alejandro: Yes. The pointy end goes into the other man.
Trivia: Joaquin Murrieta Orozco actually existed. He was a bandit in the old Spanish California during the Gold Fever; chased by a Texan called Harry Love in 1853. When he was trapped with another bandit, "three fingers Jack", both were decapitated and their heads exhibited in glass jars.
Answer: He recognized that Bernardo was really Diego de la Vega and he realized that the young Zorro he had seen earlier could not have been Don Diego. He then deduced that the new Zorro looked similar to Don Alejandro (and was probably warned by Captain Love that Don Alejandro was hiding someting) and made the decision.