Revealing mistake: In the final moments of the scene where Dracula has been confronted by Dr. Van Helsing and a cross, Dracula flees by transforming into a wolf and jumping through a window. Look closely as Dracula approaches the window and you can see the mask worn by the stuntman just before plunging through the glass.
Continuity mistake: Van Helsing and Seward discover Mina's grave empty, and go underground to look for her. Van Helsing finds her first, to discover she is now the undead. As Mina advances, Seward enters, pulls her off, and they struggle as Van Helsing grabs a stake. Mina is then "thrown" back into Van Helsing's arms, and gets impaled. As the camera pulls away, Mina lays lifeless in Van Helsing's arms as he weeps. The stake, however, has disappeared. Where'd it go? It should be sticking clear out her back, covered in blood.
Continuity mistake: In the big love scene, Dracula enters Lucy's bedroom and starts seducing her. During this it is quite apparent that some camera shots do not coincide with the moment of passion. After intense kissing, Dracula prepares to bite Lucy. The camera angle clearly shows his mouth is aimed for the right side of her neck, as he goes down on her. However, the immediate following shot shows his face still angled slightly above hers, and then he aggressively bites her on the left side of her neck.
Deliberate mistake: Despite it being demonstrated multiple times earlier in the film that vampires do not have a reflection, a key moment features the undead Mina being revealed in a reflection in water. The filmmakers said they were aware of the discrepancy but ultimately decided the visual was striking enough to bend the rules for.
Revealing mistake: [ORIGINAL RELEASE - NOT THE DIRECTORS' CUT] Van Helsing, surrounded by the men, prepares to "purify" his dead Mina after unearthing her now-'undead' corpse. As Seward and Harker question her actual state, Van Helsing holds up a small mirror for them, insisting Mina casts no reflection. When Jonathan holds down the mirror to cast a look, you can catch a glimpse of Mina's hair and some skin. (01:15:50)