When Davy Jones takes the poisoned saber and the chemist shakes his head, his close-up is flipped horizontally. Notice his hair parts the wrong way.
When The Monkees are talking Davy Jones into doubling Prince Ludlow, the close-ups of Peter Tork are flipped horizontally. Notice his hair parts the wrong way.
At 10:00 when Michael Nesmith is talking to Davy Jones while he is on the throne, the curtain behind the throne moves during a sound effect, yet no one is there and neither Mike nor Davy has touched it.