When Caspar loses at cards in the opening scene, he pushed four stacks of chips towards the old lady who won; the stacks fall over. In the next shot the croupier is pushing the now upright stacks towards the lady and one falls over. In the next shot the lady pulls four upright stacks towards her.
Penderel takes his pants off twice in two consecutive shots.
In shots aboard the ark, the main cabin is brightly lit, but in long shots of it - as when Tom climbs down from it - the cabin is dark.
The opening credits list the source as J.B. Priestley's "The Old Dark House." The original story was actually titled "Benighted."
When the stone lion falls from the gate it topples directly off the pillar. When we see it next it is fully 10 feet over from the pillar on top of Caspar's new car.
When Penderel puts on the RN Captain uniform, his cap peak is devoid of any oak leaf embossing (scrambled egg). The highest naval rank to wear a plain peak is Lt. Commander.
Many of Uncle Potiphar's animals are stuffed mounts, with the live "hyena" being an obvious wolf or dog.
When the statue falls off the gate pillar, it is clearly not a concrete pillar as it wobbles alarmingly.
When Penderel meets Potiphar, Potiphar asks him his name. Penderel doesn't tell him, but Potiphar addresses him as "Mr. Penderel" in the next shot.
When the characters encounter the coal in the basement, there is no coal dust and none of it rubs off and dirties anyone's skin or clothes - revealing it's just a prop.
If you look closely, you can see Caspar breathing while being dead.
In the opening credits, William Castle is credited as director twice: first "Produced and directed by William Castle" followed immediately by "Directed by William Castle."
When Jasper claims his mother "never spent a penny!", the dubbed word we hear is 'penny', yet the word he clearly says with his mouth is 'shilling', probably because American audiences would not understand what a 'shilling' is.
At 0:21:47 the shadow from the camera rig passes over the dinner guests.