When Lum & Abner arrive at Gold City to check out their railroad, there's a shot of a dilapidated shack with a dangling sign. This shot is flipped; the letters are backwards. A minute later, they actually walk in front of the shack; now the sign leans in the opposite direction and the letters are in the right order.
The violin case is inside the house when it explodes, but the explosion is seen to detonate on the steps outside the house.
A character is seen to hang up a phone whilst still talking to the person on the other end.