After Steve Martin gets out of the hospital the nurse turns to walk away from his limo and the driver shuts the door at the same moment the car is being started. As soon as the camera pulls back to a wider shot the nurse is gone and the driver is behind the wheel.
After Simon climbs up his stairs with the groceries, two windows can be seen on his apartment. When he sits down at the TTY terminal to chat with his daughter, the windows behind him have louvers on them and do not match the windows on his building.
During Mack and Simon's breakfast scene, the position of the napkin holder, ketchup, and sugar change during the scene. The sugar level in the shaker changes from 3/4 full to full and back to 3/4 full.