(at around 52 mins) After Ellen finishes reading Hutter's letter on the beach, she crumples the paper in her hands. In the next shot the letter is whole again.
(at around 1h 6 mins) When Nosferatu emerges from the ship's hull, the wooden "hatch/door" is not attached to anything. Moments later, a large arm hinge is suddenly attached to the right side.
(at around 30 mins) When Hutter is writing his letter to Ellen in Count Orlok's castle, the paper that he is meant to be writing on is clearly blank throughout the scene.
(at around 1h) When Count Orlok rises out of his coffin in the hull of the ship, there's a porthole right next to him and you can see bright daylight on the other side.
(at around 41 mins) When Orlok has loaded the crates onto the cart, he climbs into the last one and the lid "levitates" into place. This magic trick is achieved by stop-motion animation, but the cart horses do not hold their position and shatter the illusion (their heads jerk about completely unnaturally while the lid is in motion).
In the English-language version, modern watermarks show through the pages of the supposedly ancient "Book of the Vampires".
(at around 16 mins) When Hutter is going to bed in his room at the inn, a prop or piece of equipment being moved by a crew member can be glimpsed momentarily in the lower left corner of the screen.
(at around 1h 29 mins, Masters of Cinema Blu Ray edition), Ellen looks across the street in horror to see Count Orlok's door open and empty, implying that Orlok has already crossed the street and is in her house. Then you can briefly see a man in modern (1922) shirt and tie walk calmly into view inside the door (ie within Orlok's house).
(at around 41 mins) After Hutter has seen Orlak leave the castle in a coffin on a cart, he makes a rope out of sheets to escape, yet he was perfectly able to walk out of the castle earlier to give his letter to the postal rider.
Even though daylight is supposed to destroy Nosferatu (as it ultimately does), both on the Demeter and when he arrives in Bremen, he goes around unscathed in broad daylight.
(at around 1h 10 mins) When they show the dead sea captain with the bite marks on his neck, the individual holes are approximately 4 inches apart. Yet Orlock's vampire fangs are only about an inch apart.
(at around 1h) The captain of the ship carrying Count Orlok ties himself to the wheel with a 'granny knot', which may slip loose, rather than the correct sailors' 'reef knot'.