When Jack Buggit first asks Quoyle aboard his boat, he's gutting fish. He throws the first fish in the tub of water, and it splashes on Quoyle. When he throws the second fish in the tub, it lands on several other fish (already in the tub).
When Quoyle orders the same squid burger that Nutbeem has there is a shot of the two with a waitress in blue crossing the shot from right to left. The next shot is of Quoyle with the waitress behind him serving coffee. The next shot shows Quoyle and Nutbeem and the waitress crosses the shot from left to right. The next shot is of Quoyle once again, but the waitress is still behind him serving coffee.
While Coyle is in the diner preparing to eat his squidburger and has an exchange with Jack, his flatware changes 3 times: from being askew to the left of his plate, to being very neatly laid out to the left of his plate, and then appears neatly laid out to the right of his plate.
When Quoyle goes to his first car wreck, he views a car that had gone off the road onto rocks. However, the guard posts and cable around the curve where the car left the road are undamaged. The car could not have gotten into the position it rests in without damaging the posts and cable.
At a point in the film, Quoyle's hands are bandaged from frostbites and the bandages are later removed as he recovers. However, later when he suddenly wakes up during the stormy night (towards the end of the film), the bandages are again visible on his hands although he doesn't wear them neither in previous nor in the following scene.
Quoyle orders a squid-burger when he meets Nutbeem in the diner and the two carry on a conversation. When Quoyle spots Buggit, the camera pulls back, and shows his place setting with the burger, although the waitress hadn't returned in the meantime.
The dialogue suggests that the Quoyle ancestors were from Ireland yet the name Quoyle is very rare in Ireland. There is no letter "Q" in the Gaelic alphabet though it could have been an Anglicisation of an Irish name such as Ó Choill which is variously transliterated as Quill, Coll or translated into English as Woods (from Coill, Irish word for woods or forest).