Continuity mistake: When Willie first goes to his mom's apartment, when she is talking to him, her bra strap is on her shoulder from the front but from the back it's off her shoulder. It keeps changing position in every shot.
When "Santa" (Billy Bob Thornton) is in the bar with his mother, the bartender tells him that "smoking is not allowed in here." In the next scene, "Santa" is shown tapping his cigarette on an ashtray. If no smoking, why is there an ashtray?