Deliberate mistake: When George spies on his hedonistic neighbor down the hill with his telescope, the telescope is always level when it actually should have been pointing downward. Same when his neighbor spied on him - his telescope was always level also when it should have pointing upward.
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.