Continuity mistake: When the original Doug brings the concrete worker to fix the house for Laura, Keaton uses a red sweater with a number one on it, and a white t-shirt under; But a couple scenes later, when he is talking to number three Doug and eating a sandwich, the white t-shirt has disappeared.
Doug #2: [seeing Doug #1] Is that it?
Dr. Leeds: No. I'm afraid you're it.
Doug #2: What do you mean? I can't be it. You mean, you think I'm the clone?
Dr. Leeds: That's right.
Doug #2: I can't be the clone, I'm me. He's gotta be the clone.
Doug #1: No, see I'm, I'm me. I'm me. I'm me, right.