What does Juror THREE do to Juror EIGHT as they are leaving the deliberation room, and how does Juror EIGHT respond?

From the text:

THREE turns around and sees that they are alone. Slowly he moves toward the door. Then he stops at the table. He pulls the switch-knife out of the table and walks over to EIGHT with it. He holds it in the approved knife-fighter fashion and looks long and hard at EIGHT, pointing the knife at his belly. EIGHT stares back. Then THREE turns the knife around. EIGHT takes it by the handle. THREE exits. EIGHT closes the knife, puts it away and, taking a last look around the room, exits, closing the door. The camera moves in close on the littered table in the empty room, and we clearly see a slip of crumpled paper on which are scribbled the words “Not guilty.”