The night Ed Frazier (Howard Duff) is killed, he goes into his hotel room. The room is dark and he lights a gas lamp set in the wall next to the door. After Helen Blaine (Ida Lupino) shoots him on the road, she retrieves his key and goes to his room to find her note. When she enters the room, there is no longer any gas lamp in the wall. The room is lit up for her to search it without any light source and it is still the middle of the night.
At the end when the girl stops the stage and gets out to confess to the sheriff, after she goes back to the stage and Steve(Gary Clarke); stays alone on the shot you could see behind him on the floor what can only be black electrical cables, back then nothing but wood would've been in front of any business on Main Street.
The black electrical cables mentioned by another contributor can also be seen behind Steve when he jumps down from the judge's buggy in town (at approximately the 80-minute mark).