Continuity: Flipped shot: In the underground tunnels next to the subway, Hellboy's big arm, which should be his right, is on his left side.
Continuity: Flipped shot: When young Broom is offering Sgt. Whitman a rosary, Whitman pulls out his pistol with his left hand and offers it to Broom. The gun is a government issue M1911, but has the ejection port on the left side, and the slide stop lever on the right. The ejection port should be on the right, to direct flying brass away from right-handed shooters, and the slide stop lever should be on the left, so it can be operated by the right thumb. Left-handed versions of this gun are rare and expensive, and were not available in 1944.
Continuity: When Agent Myers talks to Professor Bruttenholm about how he's not right for the BPRD he's wearing his casual clothing from earlier in the film. In previous and subsequent shots he is wearing a black suit.
Continuity: When she is lying dead on the altar, Liz's head changes position several times.
Continuity: During his first fight with Sammael, Hellboy fires six shots from his gun. He only loaded four bullets before the fight. He subsequently fires at least another three, without ever reloading.
Anachronisms: In the picture of the WWII Army unit at the beginning of the movie, there are 2 black soldiers present. However, American Armed Forces units were not integrated until 1948, three years after WWII.
Factual errors: Although Abraham Lincoln was shot on 14 April 1865, he actually died on 15 April 1865.
Revealing mistakes: In the underground fight, the turning gates can be seen moving before Hellboy smashes into them.
Crew or equipment visible: When fighting Sammael in the subway, Hellboy is thrown into a raised window. Briefly, before smashing through the window, the wire holding him can be seen.
Continuity: In the subway station fight, Hellboy fights the monster as the train comes into the station and leaves again. In a shot a minute later, the monster swings its arm at Hellboy and the reverse shot shows the train passing behind Hellboy again. However, in shots before and after, there was no second train on the heels of the first that passes by for a split second. The shot must have been moved from the prior sequence.
Continuity: Towards the end of the movie when Myers is about to hand Hellboy the belt of grenades, the damaged control mechanism moves from his chest to his shoulder between shots.
Continuity: When Liz and Myers are on their date, he goes to get their coffee, and Liz opens her camera. Next shot, they are together, and Liz opens her camera again.
Errors made by characters (possibly deliberate errors by the filmmakers): The motto of the Bureau for Paranormal Research and Defense inscribed around the table reads: "In Absentia Luci Tenebrae Vicunt". The correct Latin should be "In Absentia Lucis Tenebrae Vincunt" to translate correctly as "In the absence of light, darkness conquers".
Continuity: When Professor Broom is talking to John and is slipping rotten eggs into Abe Sapien's tube, he puts only one egg onto the small platform, but when we cut to him snapping the platform into the tube, there are now two rotten eggs, and two again when Abe is eating them in the water.
Continuity: At two different times, it is stated that six guards have died in the museum. Yet, when Abe shows Professor Broom what happened, we see seven guards killed by Kroenen. Two on the catwalk and five on the floor with Kroenen.
Factual errors: The scrap of paper that the professor finds on Kronen's body does not say "Sebastianplaskva" in Cyrillic.
Continuity: Before confronting Broom at the BPRD, Kroenen wound the mechanism in his chest counter-clockwise, which should have caused him to deactivate as it did when he wound it counter-clockwise before Hellboy finds him in the tunnel. In all other scenes he winds it clockwise before he sees action.
Continuity: Ilsa has blood on the left side of her face after John kicks her. The blood disappears when she bends to kiss Rasputin, and then reappears after she withdraws.
Continuity: Hellboy is fireproof. He isn't affected by fire in any of the scenes in the whole movie. Yet after Hellboy emerges from under the train in scene nine, he touches his stunted horns which are now scolding hot and reacts in pain.
Continuity: In Rasputin's lair, Hellboy and Manning are proceeding slowly and carefully through a narrow passage lined with spikes, not only to make it through without being hurt by the spikes, but to sneak up on Kroenen, who is sitting in a chair in the room at the end of the passage listening to music. Manning negates the possibility of either of these things happening when he cuts the back of his left hand on a spike and exclaims "Ouch!", which Kroenen hears. However, when he and Hellboy make it into the room and see that Kroenen is no longer sitting in the chair, Manning says to Hellboy "Hey, it really went deep", and shows him the bloody cut, which is now near the tip of his left index finger.
Continuity: On the Bridge scene under the graveyard, Tom Manning is thrown and slides under the door just before it closes. However Hellboy also slides under later in the scene when the door should have already been closed.
Revealing mistakes: When Agent Myers was at the gates of the Bureau for Paranormal Research and Defense, he had a retina scan. The machine scanned his right eye, but it identified it as his left eye.
Continuity: In the library, when Hellboy was walking into the crime scene, there were only three glass display cases in the center of the room, but when the monster threw Hellboy through the cases, Hellboy crashed into four cases before hitting the window
Revealing mistakes: When Kroenen is fighting off the guards during the museum scene, as he moves his arms around, the knife and sheath on his upper arm bends and twists significantly, revealing that the prop is made of rubber and fiber-glass.
Errors made by characters (possibly deliberate errors by the filmmakers): Flubbed line. When Abe Sapiens reveals a number of facts about Myers, Myers is then supposed to say, "how did it ..." and subsequently be corrected by Prof. Broom, "he, Abe's a he." The subtitles have him saying it but if you listen Myers says "he" in the first place.
Errors in geography: Just after the opening credits we see what is later revealed to be Ilsa, Kroenen and a guide in a snowy, rocky setting which is described as "Birgau Pass, Moldavia" in the caption - Birgau, or Borgo (a popular location in vampire lore), is in fact in Romania.
Factual errors: The shadow of the Earth on the Moon is the same diameter for the eclipse. The Earth's shadow is much larger and would inscribe an arc on the moon aside from the Lunar eclipse taking hours instead of minutes.
Continuity: When Kronen is first seen, he raises his arms and his blades rotate around like clock hands, from mechanisms obviously on the outside of his sleeves. Later, when he tries to retrieve the grenade, he clenches his right fist and the right blade retracts straight up his forearm, the mechanism beneath his sleeve.
Factual errors: Mike Mignola's claims that Hellboys's Samaritan revolver weights nearly ten pounds yet when he spins it, it spins rapidly. A revolver of that weight would have a poor balance, causing it to spin subsequently slower (even for someone as strong as Hellboy, the balance would play a heavy factor).
Continuity: Abe has webbed fingers, yet in all the scenes where he is wearing gloves he has normal human hands.
Continuity: When Hellboy is under the train, he keeps getting smacked on the lower edges of his horn stumps. When he stands up, it's the upper edges that are glowing red hot from the impacts.
Continuity: When Hellboy stops the car by slamming his hand into the bonnet and flips the car, the grille and bumper are seen to break off the front and as it flips over the grille about to fall on Hellboy, but when the car lands the grille and bumper are nowhere to be seen.
Continuity: Underground, just after Abe is injured underwater, and the two agents are killed, Hellboy is walking into a room. As he enters, his RIGHT hand is normal and holding his gun. Just after he approaches the table, now, his LEFT hand is normal and holding the gun. His large hand has changed sides.
Continuity: In the scene where Myers and Hellboy take cover from Samael behind the dumpster Hellboy's hand has no stinger on it when he hands the Samaritan to Myers. But when he reaches back to grab the gun the stinger is suddenly there.