Continuity mistake: Hugh Jackman puts a tan vest on twice in the scene when we first meet his wife.
Revealing mistake: When one twin (presumably Alfred) is removing the other twin's fingers, "Alfred's" upper arm passes through his twin's head as "Alfred" reaches for the hammer. [Fixed on DVD.]
Visible crew/equipment: When Angier goes to Tesla's laboratory and walks to the gate, on the far right side of the fence a figure can be seen, apparently holding something ahead. It seems to be one of the film crew holding a boom mike upright. (00:09:59)
Continuity mistake: When the hotel clerk show Angier Tesla's machine in its box, he has his hands behind his back, and then moves them in front of his body. Yet when the camera cuts to behind the clerk, his hands are still held behind him.
Other mistake: This mistake occurs when Borden crashes Angier's act. Borden emerges from the trick door for the Transported Man trick, feigns surprise, and then "discovers" the bound and gagged double suspended above the stage. When Borden says "Ah, the Great Danton" you can see the ring and pinkie fingers on his left hand moving, even though he had already lost them by this time in the movie. We know that it has to be after the time BOTH twins lost their fingers because Olivia observed Borden's trick and says that "it is the same man" because she was fooled by both Bordens having their gloves stuffed.
Visible crew/equipment: In the final shot where Angier lies dead on the ground with the theatre on fire, the camera can be slightly seen reflected on the glass box with one of many Angier's doubles inside once it does a tracking shot. (02:04:52)
Factual error: When Angier and Cutter are looking for a new workshop they enter a room, with a fully glassed wall on one side. A very modern white radiator is in the room. (00:35:00)
Answer: Angier always wants to take revenge on Borden as he is the reason behind the death of his wife. He knows that Borden is in the crowd the two times, first time, Olivia suggests Borden to watch the new "Transported Man" trick of Angier, where Borden finds out the trap door in the bottom of the machine, second time, Borden wants to know how Angier flies that distance with in seconds through the trap door. As expected by the Angier in the final play, Borden reaches the back stage where actual Angier is drowning (it is as always actual Angier drowns and the replica of Angier appears at some distance in every performance). So, as per the plan the replica hides to create an impression that Borden intentionally murders Angier. Note: the replica of Angier has the same ability and sense like actual Angier.
Rajesh v
It's never stated whether the "real" Angier drowns or takes the bow, but it's implied that it doesn't matter - as the clone is a perfect copy, they are both "Angier." Angier at one point says, referring to toll the trick has taken on him, that each time he did it, even he himself didn't know whether he would be the man in the box or the prestige. Similarly, when Angier asked Tesla which hat of all the duplicates was his, Tesla replied "They are all your hat."