When Thomas Cole knocks on the door of Paul Benjamin's apartment on his first visit, Paul goes to answers the door without a cigarette. However, when he opens the door a lit cigarette appears in his mouth.
Auggie takes his daily picture from a typical tripod, below shoulder level. Yet the photos in his album are taken from eye-level position or higher. In fact, the alignment of the traffic signal and the building behind it is so consistent from picture to picture, that they were most likely taken from a fixed mount.
The Coke cans throughout the movie have a Six Flags/Great America admission advertising on them that did not exist on coke cans in 1990; the first came along in 1993.
When Ruby (Stockard Channing) and Augie (Harvey Keitel) meet in the tobacco shop for the first time, Ruby's left eye can occasionally be seen underneath the black eye patch. The character is said to have lost her glass eye.