Just as Dolores gets home from getting the afternoon off from Vera's, Joe steps up onto the porch. His left pant leg is ripped showing his thigh, but when he's chasing her through the yard his right pant leg is ripped.
In the first flashback, the shadow at the top of the stairs shows Dolores standing when Vera falls down the stairs. In the second flashback, it shows Dolores on the ground when Vera tumbles down the stairs.
When Selena telephones Peter, the cuffs on his sleeve alternate between being open and being fastened.
During the flashback scene in the kitchen which culminates with Joe hitting Dolores across the back, the thickness of the roll of kitchen paper hanging underneath the cupboard behind Dolores changes drastically at one point.
In the first flashback of Vera falling down the stairs, her back hits the railing, but in the second flash back, when they show what really happened, her back is facing Dolores, who is standing at the top of the stairs.
A scene shows Dolores driving the night before a total solar eclipse. The scene shows a full moon, which is impossible since a full moon cannot occur less than 14 days before a total solar eclipse.
Since Delores worked and lived in Vera's home, one would expect to find her hair, blood and DNA (if DNA testing was done at that time) in the home. So the hair and blood samples collected by the detective would not help to prove Delores murdered Vera. Furthermore, the postman came into Vera's home every day at noon, his DNA would be in that house as well.
When hair samples are taken for analysis, they are pulled with the root intact, however, several are taken from different parts of the head/body.
In the beginning of the movie, when Kathy Bates returns to her home, she swipes off pieces of glass on the outside of a window. Apparently the window was thrown in by an object from outside. Glass pieces would have been on the inside of the house.
The eclipse is dated early in the movie as occurring in 1975. However, according to the NASA Sunsearch database records, there were no solar eclipses (total or annular) on Earth in all of 1975. Additionally, from 1961 to 1980 there were no total eclipses visible in the filming locations. The closest was visible only in the Pacific Northwest in February of 1979.
When Selena reveals her secret to Dolores on the ferry boat, another boat passes by which uses Global Positioning System (GPS). GPS did not become commercially available until the mid-1980's.
When Selena is driving away from the house she discovers a mini-tape Dolores stuck to her laptop, when she takes it off it's suddenly a regular cassette tape that she can play in her car.
When Vera is elderly and bedridden, being looked after by Delores, she is shown to have no teeth at all and her voice has a lisp because of this. Between shots, she suddenly has teeth and is even able to bite Delores' arm.
As Dolores and Selena are leaving the police department, they walk across the street and get in the car. As Selena opens the door, the telescoping crane can be seen reflected in the car window.
In several shots of Selena driving into town, the camera mounted to the hood of the car is reflected in her sunglasses.
After the brief shot of Dolores turning over her glass on the tabletop and booze dripping out, it slowly dissolves into a shot of clouds, then a pan of the shoreline to reveal the St. George house. During that pan, a portable toilet is very visible. A company in Nova Scotia rents a model that is blue with a bright yellow roof - exactly what you see in the scene. That's a fairly distinctive color scheme, which arguably makes this a geographic goof as well.