The left gauge on the oxygen tanks indicates "10" when the doctor examines it, yet it indicates "2" before and after his verification.
When Perry and Della first pull up and park at the Davenport real estate office, Perry sloppily parks his car at a poor angle with the left front wheel across the line into the next closest right parking spot.
When the secretary and police officer pull up and park later, Perry's vehicle is parked in the parking spot perfectly within the line markers.
When Perry and Della explore Davenport's office, the dialog indicates it's nighttime. But all the outside parking lot scenes are obviously shot in daylight.
Ed Davenport pulls up to a cabin in a motor court and walks right in. Despite the fact that he has not checked in, the door has been left unlocked.
In Perry's office, early on, the real Louise refers to Myrna as Louise, just after she says, "Well, there's something that I haven't mentioned..."