Pifias

In most shots, Robert Reed (6'3") is visibly taller than co-star June Kenney (5'2"). But in some scenes (eg, when they are exploring the mansion), she appears to be only a few inches shorter than he is.

When Jondor lifts the blind covering the case with the girl suspended in formaldehyde, her head is tilted towards the camera, but in the close-up it is facing the bottom of the tank.

After shooting the insane man with his crossbow, Dr. Balleau pulls the bolt out of the man, cleans off the blood and carefully places it back on the crossbow. But, he has failed to draw the bow string back beforehand leaving the crossbow useless. In the next scene, the crossbow is shown as cocked and ready to fire.

Obvious male stand-in when Betty flips Balleau's henchman into the boiling water tank.

The crossbow string is fully drawn back & locked, but the arms are not bent backward so there is no tension to fire the bolt.

In the scene where Belaeu shoots the small horse statue to illustrate the deadliness of his crossbow, you can plainly see the fake bolt (arrow) hanging in the air a few inches away from the just shattered statue - a moment later it's stuck in the wall.

Pete steps into quicksand nearly up to his waist; when pulled out he has leeches all over his chest under his shirt, with no explanation as to where they came from.