Wilson comes in after jogging and his green shirt is obviously sweaty on the back. He surprises Barbara and Stanley in the room and punches Stanley in the face. Stanley goes into the bathroom and when Wilson follows, there is obviously no sweat marks.
The wetness of Sheila's hair in the bathtub with Stanley.
James Whitmore's glasses keeps pushing his glasses back up his nose throughout the introductory speech, sometimes seconds apart as the cameras switch between long and close up shots.
The boom mic is visible over Beth and Stanley as they discuss the initial improvisation exercise with the professor.