Goofs

When Sid James displayed the broken telephone wire when trying to ring the police, his hands have jumped from holding the telephone wire straight into his pockets.

Ernie, Syd and the butler go out into the pouring rain to check the generator, but when they enter the outbuilding they are completely dry.

Fisk carries a torch to inspect the generator, but the position of his hand varies greatly between shots.

When Everett Sloane first meets Ernie Broughton in his room, he removes his bowler hat and their is a tuft of hair sticking up at the back side of his head. In the next shot however, his hair is perfectly groomed, until Sloane stands at the door to leave and the tuft is there again as he replaces his bowler hat.

Ernie is supposed to be a proof reader but the book he is reading has been published, far to late to be proof read.

Sloane comments after examining the dart that it is Curare, the pigmy poison but Curare is indigenous to South America and Pigmies who always considered to be from Central Africa.

As the "dead" body of Everett Sloane goes into the fish-pond, he puts out his arms to protect himself.

We see Ernie proof-reading the (fictional) novel "The Fiend of the Second Floor Flat", but the spine of the paperback used as the mock-up doesn't match this title.

(at around 76 mins) When the recently murdered Guy Broughton falls face forward to the floor, his eyes distinctly move downwards to check that he has a safe landing place.