Continuity mistake: Near the beginning Harriet Vane produces tokens for herself & Lord Peter Wimsey of miniature handcuffs with one cuff "open to symbolise we're giving up on crime". She puts hers on as a bracelet. Immediately after & several times throughout the film it's clear hers is a set of closed handcuffs.
Continuity mistake: When the girl helps Frank by licking a stamp and putting it on an envelope, Frank gets up from the table, holding two pieces of folded paper in his right hand and goes to the filing cabinet to get a folder out, with the papers still in his right hand. When he goes to return to his seat, the papers are now in his left hand.