Continuity mistake: Frank's whiskey glass and napkin coaster are about a foot away from the bucket as Dennis is explaining why he is fasting. When the camera cuts to Frank as he says "Forget it," the glass and napkin are suddenly right next to the bucket.
Continuity mistake: When Mac asks Charlie "The good Lord is coming down on you, what's that supposed to mean?" the guy in the background with the walking cane and hat is walking away, almost to the end of the bar. When the shot comes back to Mac the same guy with the walker and the hat is right behind him again, strolling off into the same direction.
Continuity mistake: When Mac asks the old guy if he wants a blessing, the man in the background holding a newspaper and rolling walker is about to talk to the black guy sitting at the bar. After Mac and Charlie fight over who is better equipped to give a blessing, the man in the background with the walker and newspaper is walking up to the guy at the bar again.