At the 29 minute mark, when Frank is in the coffee shop talking to Gabby, her hand position changes from the side of her head to behind her neck between camera angles.
When Frank emerges from the hatch in the desert during the escape, in the far left corner of one of the shots you can see the sail of a terra-sailor moving across the horizon, a windsurfer with wheels. A popular activity at the El Mirage Dry Lake where the escape sequence was filmed.
The set was constructed with recycled items and in certain shots, the "Dr. Pepper" labeling is visible on the plastic crates that are used to create the walls of the prison cell.
When Frank leans into the bathroom before his escape attempt, gaffer's tape can be seen on the doorway, holding the set wall together.
From the 6' mark forward, when Frank has his first conversation with Howard, one can see one or two persons moving behind him, in the dark reflection off the glass plate in front of Howard's camera lens.
When Frank crawls out of the hatch in the desert, dolly tracks can be seen in the sand as the camera pulls back.
When Frank first decides to "sit this one out" at the coffee shop, a reflection of someone walking in the background is visible on one of the photographs behind him, even though the only people in the coffee shop are Frank, the waitress, and the sitting patron with the brown jacket. Nonetheless, this may possibly be a reflection of someone walking outside the store as the next scene shows a reflection that looks more like a car driving past.