During the fight between Hellboy and the three giants, Hellboy's "rock" hand switches from the right hand to the left hand then back to the right hand.
In a shot of Hellboy riding in the back of a limousine from the airport to the Osiris Club, the back edge of the window beside him is almost vertical, with rounded corners. When the limo arrives at the Osiris Club a shot from outside the limo shows that edge noticeably slanted, with angular corners.
When Hellboy is sitting in the helicopter heading to the BPRD, his horns are properly filed.
When Hellboy wakes up at Alice's apartment, his hair goes from all down to a half bun by itself.
When Hellboy first arrives in England and is on his way to the Osiris Club, the car is shown driving through the countryside on the right side of the road. In England, it should be on the left side.
Hellboy wouldn't be able to remove his long coat as the sleeve doesn't fit over just big arm.
The Land Rover driven through London about 3/4 of the way through the movie has the registration YD17MRB. If you check this,it turns out it's on a motorcycle, a Triumph Bonneville Bobber.
At the start when Hellboy has the spotlight shining on him near the wrestling ring, he has fairly smoothed off horn stumps. A few minutes later when he is drunk in the bar, he has very jagged horn stumps.
It is revealed that three weeks has passed between the wrestling match and the bar scene, allowing for both horn growth and a lack of filing down or cutting.
It is revealed that three weeks has passed between the wrestling match and the bar scene, allowing for both horn growth and a lack of filing down or cutting.
During the battle with the three giants, the zipper on the back of David Harbour's Hellboy muscle suit is briefly exposed when his trench coat flips up.
When Hellboy is filing his horn stubs one of them wiggles.
When the Osiris guards are zapping Hellboy they are standing in the river. At that proximity and being grounded, they should be getting zapped as well.
When Hellboy, Alice and Daimio are in the helicopter, heading to Pendle Hill, Hellboy comes forward and puts his hand on Alice's shoulder, you can see that it's actor, David Harbour's hand in its natural color and form, with no red make up to make it Hellboy's hand.
When Hellboy is ambushed he has a spear noticeably sticking out the front and back of his body. He falls off a bridge and lands flat on his back on the ground below. As he gets up to run away the spear is sticking out both sides at the same distance as before the fall. This shouldn't be the case since the back portion just got drove into the ground.
At the beginning of the movie when Hellboy is on the phone, you can clearly see that he has neither answered or declined the call despite having a conversation.
During the flashback scene with Alice's parents, the demon is seen escaping up an open fireplace. It was already established in an earlier scene that Alice lives in a London tower block so an open fireplace could not exist there.
In the flashback scene with Major Ben where we see how he got his abilities, he is shown holding an M16 rifle. This is not a weapon that the British army use.