In the opening scene in Paris, when Van Helsing picks up the wanted poster,the Eiffel tower is seen in the background only half built, however, when on the roof of the Cathedral, while Hyde is holding Van Helsing up, the tower can be seen fully built behind them.
When Van Helsing fights Mr. Hyde in the second scene of the movie, Mr. Hyde steals his hat. Later, Van Helsing takes his hat back. Then, when he is thrown off of the roof, he loses his hat again. When Mr. Hyde falls and the police find him, they look up to the roof to see Van Helsing standing there, putting his hat back on. How did he get it back?
When the werewolf returns to Frankenstein castle and starts climbing down the walls, it isn't wearing any clothes. When it lands on the ground and starts changing back to Velkan, it is suddenly seen wearing tattered pants.
When Van Helsing and Anna flee Frankenstein's castle, it's full moon. Their trip to Budapest then takes them better part of a month, since by the time they get there, it's only two days to the next full moon. And yet it only takes them a day to get back to Anna's home castle.
When the brides hide from the sun in the village well, Anna slowly gets up. The camera angle shows behind her a few people hiding and a wooden bench. The scene cuts quickly to Van Helsing and back to Anna to reveal a dead body that wasn't on the bench before. As well the dead body's eye can be seen moving while closed.
Anna is wearing a tiara at the masquerade ball while dancing. After Van Helsing brings her up to the balcony, Anna's tiara is missing. Actually, Anna's tiara fell off her head when they landed on the balcony.
At one point in the opening, Dr. Frankenstein is packing a trunk. When the scene cuts to the villagers and then back to Dracula and the Doctor, the trunk seems to disappear. It can in fact be briefly seen off to Dr. Frankenstein's left when he and Dracula are looking over the monster. Since it is implied that Dracula and the Doctor had a conversation between shots, they would have had time to move away from the trunk.
The glass of blood one of the Brides drinks leaves a pulpy residue on the glass - a trait of tomato juice.
When Van Helsing bends the metal bars blocking the way to the monster the bars are clearly made of some softer material. This is obvious since they start bending before the effort starts to show on Van Helsing's face.
The horses fail to react in any manner whatsoever to Van Helsing jumping and crashing into them (caused by real horses and a CGI-produced actor).
When the Cardinal and Van Helsing are walking into the lair for the Knights of the Holy order, if you look in the background you can see a reflection of Cardinal's robes, revealing an old film technique of using mirrors to make rooms look bigger.
Obvious stunt double when Anna jumps through the window with Van Helsing.
At the time the movie takes place Transylvania did not belong to Romania, but to Hungary. It only became part of Romania in 1919-1920.
Van Helsing throws Igor on top of a rock and interrogates him. When he lifts Igor off the rock, you can briefly see several sheets of white paper, stapled or paper-clipped together, on the rock. It's probably a script left there by the actors.
At the ball, when Anna says, "You make my skin crawl," her mouth doesn't move.
When Van Helsing and Anna are fighting the vampires in the village, when the sun has just come out, and they hear a noise from the well Anna bends over to pick up her weapon from the ground. As she picks it up it makes a metallic scraping sound even though there shouldn't be anything metal in the ground for it to scrap against.
You can see two crew members kneeling down behind the bull, holding it steady.
The map shows the path of the coach heading south of the Carpathian mountains toward Budapest while the city actually lies straight to the west
When Anna and Velkan are fighting the werewolf at the beginning of the movie, there are about a dozen people helping them. Who exactly are these people, and where do they disappear to for the rest of the movie, when Anna could have used more of their help?
When Velkan and Anna are trying to capture the werewolf, Velkan's gun is the only one that has silver bullets and thus the only weapon capable of killing it. Why didn't all the people involved have weapons with silver bullets in case something went wrong?
Aleera confronted Anna and Carl in the chamber of the werewolf cure and saw Carl running away with it. Yet she did not try to figure out why they were after the cure in the first place especially since Valken was dead. Surely Dracula told his brides why he needed to have the werewolf cure on standby.
Carl, at least twice in the movie, indicates that he's not a Monk but "just a Friar," the implication seeming to be that Friar is one step to becoming a Monk, which is untrue, they are two separate vocations in the Catholic Church. Monks live in self-sufficient, cloistered communities. Friars live, work, and minister among the people. Further, the implication of being "just a Friar" is misused as justification for Carl's cursing toward the beginning of the film, and suggesting a sexual liaison later on. Friars are either ordained priests (think Robin Hood's Friar Tuck), ordained deacons, or they are vowed Brothers. None of these are "allowed" to curse (any more than any Christian), and all of these (except some Deacons) are celibate.
When explaining the lack of feeling and emotion, Dracula is obviously VERY emotional.
In the prologue, the grave digger has an English accent. Later in the film, he speaks with a "Transylvanian" accent.
Carl says that the Battle of Masada was in "73 A.D." 'A.D.' is an abbreviation for the Latin 'Anno Domini' -- "In the Year of Our Lord". It is always written or spoken before the year mentioned (A.D. 73 = In the Year of Our Lord 73). 'B.C.' is said after the date. 73 B.C. means '73 years Before Christ'.