When Dirk is inviting Grace to dine with him, he shakes out a napkin and tosses it on her plate. We then see the napkin on the plate neatly folded in a triangle shape.
When the killer confronts Grace, Dirk and Maudie under the city, the trio change positions between shots.
When Grace and Dirk toast Victor at the pub, Grace takes a drink from her glass. When she sets it down, it's full again.
When Max, Dirk and Grace are eating breakfast in the diner, the glass Grace is holding changes positions between shots.
When Maudey fires Dirk's pistol at the serial killer, the blast propels her off of her feet. In reality, this type of gun lacks the kind of blow-back power to do this, even in the case of a dwarf.
When Grace and Maudey order Guinness (like Victor Fox's last drink) in the bar, the glass is filled in one go and immediately served to them. Guinness is never poured in one go. The three quarter full glass is left for a couple minutes for the froth to settle, then topped up and served. Also the color of the beer in their glasses is too light for Guinness.
When Grace walks towards the piano. Sally Jessy Raphael said "Ladies and Gentlemen Grace Beasley. Amazing Grace" when Sally is shown her lips weren't even moving.
When Grace collapses on hearing that Victor Fox has been murdered, she drives her shopping cart into a display of Orange Slice soda. The sodas are clearly in plastic bottles, but the sound effect is of glass bottles being knocked over.
When Dirk and Grace go to the funeral home to "dress up" Victor Fox's corpse for the open-casket funeral, the funeral home manager is hesitant to allow them to enter until Dirk introduces Grace as, "This is my lawyer..." In England, Dirk would probably not have used the word "lawyer". It is more likely that he would have said, "This is my solicitor..." (although, in mitigation, the word "lawyer" is widely used, and even solicitors and barristers often describe themselves as lawyers).