When Zosh runs out onto the back beck of the apartment, she stops by a post to make her last stand. She blows her whistle and falls backward and to her right, and no post can be seen. When the scene cuts to her falling, she's now in the middle of railing with the post nowhere near her.
Zosh's scrapbook is titled "My Scrapbook of Fatal Accidence" (instead of "Accidents"). This is very possibly not an error. Zosh could be poorly educated, or simply be a bad speller. When Frankie first enters the apartment, after his stint in rehab, she has a sign waiting for him that reads, "Wellcome Home Frankie. Not only does she misspell "Welcome," but she also uses a lowercase "i" when all the other letters are uppercase.
In a scene about twenty minutes in, as the camera exits the bar following Frankie, the jukebox can be seen to slide out of the way of the camera at the bottom of the screen.
When the first responders pick up Zosh's lifeless body from the street, her body remains perfectly stiff, revealing that a board must have been placed under the actress before the scene was filmed. A dead person's body would sag in the middle when lifted by two people on either end.
A heroin addict is shown in jail going through withdrawals. Normally, the first thing which occurs are physical symptoms, like vomiting, running a high fever, cold sweats, etc. This man grabs the jail cell bars and screams " I need a fix!" over and over. This is not authentic. So bad, it is like a cartoon.
In the first scene between Frankie and Zosh, the shadow of the camera is frequently visible as it moves around the set.
When Frankie returns to his apartment after his release, the top edge of the set and the studio lights are clearly visible as the camera pans across the room.
At the start of the the scene where Frankie is forced to return to card-dealing, the boom mic can be seen near the light fixture.