Goofs

When Peregrine Devlin arrives at the fencing school, you see him attach a cable to the back of his fencing kit (which would signal a hit with a buzzer), yet when the other fencer reveals himself to be Edward Lionheart and they start fencing, the cable is no longer attached to Devlin's back.

When the decapitated head of Horace Sprout is discovered by the maid on his bed, the eyes are closed. After it falls on the floor, the eyes are open.

There is blood already on the plastic sheeting prior to George Maxwell being stabbed.

The pie served to Meredith Merridew changes in size between shots.

The blood that appears on Trevor Dickman's body when he is cut by a knife does not match the movement of the knife in the previous shot.

Horace Sprout's decapitated head rolls over when the maid discovers him. In the next scene, it is impaled on a milk bottle at Devlin's front door. It has been said this is a goof because Lionheart could not have retrieved the head after the maid saw it the next morning. But the head left in the bed was a "dummy" waxwork head. Lionheart took the real head and put that on the milk bottle at Devlin's front door.

During the film's fencing scene, someone in the background can be seen looking through the window of the gymnasium's door.

This could simply be a member of the fencing club looking in the window and wondering why people are fencing when the club is supposed to be closed.

When Lionheart is trying to trick the police with a man masked like him, it is clear that it is the real Lionheart who is driving past the police when they notice him.

The way Solomon Psaltery makes a hole in the door with his hand would not be possible, revealing that the door is a prop.

Obvious stuntman for Vincent Price when Lionheart is climbing the burning building. Edwina's corpse is very likely a doll.

The thing used to gag Miss Chloe Moon would not have stopped her from screaming for help because it was too small.

The wine in which Larding is drowned is clearly colored water.

Obvious wire when Lionheart is carrying Edwina's corpse and walking atop the burning building.