In the scene in the cattle pens when Max (Steve McQueen) fights Jessie Coe (Martin Landau), Max crouches behind a fence and opens the gate to let the cattle out. Some cattle come out the gate while others knock down the fence, and Max must dodge the flailing legs and hooves of the stampeding cattle. The knocking down of the fence was accidental, and McQueen was very nearly trampled for real. Shots of Max rolling clear of the hooves were added when it was decided to use the accidental footage.
The name "Nevada Smith" was the original inspiration for the name "Indiana Jones"; the Raiders of the Lost Ark (1981) character's name was originally "Indiana Smith". George Lucas named him "Indiana" after his dog, and "Smith" after this movie. But then it was changed to "Indiana Jones".
When Keith is teaching McQueen poker and McQueen pulls the gun on him, Keith's gun vanishes from his right hand between shots and the whiskey bottle changes from his left hand to his right.
After waking up on the pool table Smith orders a drink at the bar. When the bartender pours the drink Smith puts his hand on the glass. In next shot Smith reaches to pick up the glass.
The camera's shadow can be seen as it pans across several head of cattle being driven in the scene immediately following the parting of ways between Max and Jonas.