Revealing mistake: When Count Orlok has loaded the crates onto the cart, he climbs into the last one and the lid "levitates" into place. This trick is achieved by stop-motion animation, but the cart horses do not hold their position and shatter the illusion - their heads unnaturally jerk about while the lid is in motion.
Plot hole: When Nosferatu is caught in the sunlight towards the end, his reflection can be seen in the tall standing mirror in the corner of the room. This makes no sense because vampires do not cast reflections. Deliberate or not, in the original Bram Stoker novel, there is a scene in which the character Harker is shaving, and is disturbed to see that the Count casts no reflection. There is also a passage that states, "He throws no shadow, he make in the mirror no reflect." Some would argue that the rising of the sun robs him of his powers, giving him the reflection. But his reflection is visible before the rooster starts crowing, before the sun even rises.
Continuity mistake: When Ellen dies on her bed at the end of the film, she collapses on the pillow and her head is looking upwards, but in the next shot, her head is now facing left.
Continuity mistake: When we first see the dead ship captain, his eyes are half open. When they find the captain behind the steering wheel a little later on, his eyes are closed.