Both cue balls move a few inches back and forth between camera shots. It's best seen by watching the one near Sam; in some shots it's lined up with the corner pocket and other shots it isn't.
In the first scene after the opening credits, in the bar, Rebecca talks to the guys.
The camera cuts to Sam just as the bar door opens.
A man wearing a yellowish top accompanied by a woman wearing a black and gray top walk in.
About 20 seconds later the camera cuts to Sam again. The same two people are seen opening the door again.
Around 80 seconds later the camera cuts back to Sam showing the pair STILL entering the bar.
Sam's darts moves from the edge of the pool table to being on the pool table from one scene to the next.