When Johnny has the shootout with Bart in front of the hill-top cabin, Vienna is standing on the deck of the cabin, her body all the way to the timber railing. She is in sunlight. Then the view of her goes to a closeup, but now she is standing inside the door opening, in what is obviously a studio shot. This is probably connected to the fact that Joan Crawford insisted on her closeups only being filmed in the studio, where the lighting could be rigidly controlled. No closeups of her were shot on location.
When the posse rides through the waterfall, Emma Small's clothes are bone dry even though she already passed through the waterfall earlier.
In the first long scene, ostensibly one uninterrupted time sequence, Vienna wears three very different shades of lipstick: first a bright magenta, then a dark tomato red, then a medium carmine shade.
Emma rides through a waterfall to speak to Bert, but later when she's waiting with the posse, she's dry. She and the posse pass through the fall, and she's wet at first while the posse isn't, then her hair is wet but not her dress.
Near the end of the movie, Vienna and Johnny are talking on the bridge. In the background the sun is nearly set. In the very next scene it is bright daylight as the posse searches for them.
At 48:56 the background painting can be seen. The horses and stage coach come to a stop with the bottom of the backdrop just above the plane of vision over the horses, directly bordering the cast shadow of the building at the right.
When Emma halts on the bridge, in front and to her right is a pile of horse dung. Besides a view of excrement being against the propriety rules, it means that a horse was stopped at that spot for a brief period of time and left a prominent sign of a rider passing, which does not happen when fleeing a posse.
After the bank robbery, Vienna and Johnny Guitar are riding along in a buggy drawn by a single horse. While the horse sounds like it is only trotting along, the scenery rushing past the buggy makes it appear the buggy is going at highway speed.
When Lou from the posse says that he's panned every inch of the stream, his lips are out of sync and the sound quality doesn't match the rest of the sound. It is clearly studio dubbed. However, his lips do say exactly what he is heard to say; no words are changed.
A boom shadow can be seen at the top of frame, as Johnny waits for Vienna to change clothes in the mineshaft.