When the cowboy gets a beer from Joe, he drinks almost all of it, but leaves about an inch at the bottom in each glass. But, when he scoops up all the glasses on the table and takes them back to the bar, they are almost all completely empty.
There is about a second that elapses between the time the old cowboy fires his gun and the bullet breaks the light.
Joe points his gun at Blick and pulls the trigger. And when it doesn't go off he says "That dumb Tom. He buys a six shooter that won't even shoot once". Even though he knows he loaded and unloaded the gun early in the film. And it happens to be a gun that only holds 5 cartridges.
When Nick goes to the betting parlor to see the broadcast of the horse race, the man at the door opens it before his hand gets to the knob on the lock.