Frank fills the coffin with the plants that were covering it, but after he falls into the water, there is nothing in the coffin.
During the fight between Frank and Alucard the coffin is still pretty much undamaged, but after Alucard dies and Frank leaves, there is almost nothing left of the coffin.
Prof. Laszlo says, "In Transylvania, the name [Dracula] is associated only with evil." This is not true. In fact, the historical Dracula (Vlad Dracula) is considered by many to be a national hero.
This film does not take place in the same continuity as Dracula (1931) and Dracula's Daughter (1936). Dracula's back-story in the film follows the Bram Stoker novel rather than any earlier film.
When Alucard/Dracula approaches the bedroom of Colonel Caldwell, and transforms from bat to man, both the bat and Lon Chaney Jr. can be seen reflected in a mirror hanging on the wall, which is a no-no in Universal vampire lore, as vampires cast no reflection. What's more, the actual animated transformation is not reflected; rather a jump-cut is seen in the mirror.
When Count Alucard walks toward Colonel Caldwell's room, he casts a reflection in the hallway mirror.
When Doctor Brewster is reading a book about Dracula, the page he is viewing consists of the same two paragraphs repeated throughout the two pages.
Lon Chaney Jr pronounces the ending D but "Alucard" is a French word and ending consonants aren't pronounced as there is no vowel following them to pick up any sound, that's why they're not pronounced. Comically enough, the word's turn then sounds much like "à la carte" (a-la-card).
When Frank leaves the house to go riding, he passes a window, in which the boom mic is momentarily reflected.
After Dracula falls into the water, his hand is already grasping the tree root, but in the next close-up, his hand reaches up to grasp the root.
After Katherine bites Frank and gives him immortality as a vampire why would he then set her on fire?, ensuring he has to spend eternity without his woman.