When John Proctor and Elizabeth are having their private conversation towards the end of the movie, his teeth look normal. However once they return to judge and Rev. Hale, his teeth look rotted and decayed. When he his hanged (the same day) his teeth are normal again.
After John Proctor runs into the pond outside the church, his hair goes from being totally soaked in one shot to completely dry in the next.
As John Proctor holds his confession note, the condition of the paper changes between shots from being almost completely crumpled within his hand to mostly exposed and barely wrinkled to mostly exposed but extremely wrinkled.
When some of the townsfolk throw a knife in Reverend Paris's door, the knife is shown to be perpendicular to the door. In the next shot when the door opens, the knife is on an angle.
When Elizabeth Proctor is being brought to the court, the left rear wheel of the cart is not spinning.
The word "pregnant" would not have been the choice of word in the 17th century for a woman with child. That would have been not an appropriate way to describe the condition. It is spoken twice.
In the scene where John Proctor goes out into the pond, when the camera cuts back to the crowd onshore, an airplane condensation trail can clearly be seen in the sky.
When Abigail Williams meets with John Proctor behind a house, the house's siding has modern round-headed nails instead of cut nails used at that time.
John Proctor uses the scythe incorrectly. A scythe is drawn right to left in an arc parallel to the ground. The stroke requires neither great physical strength or blade speed. However, Proctor, with much effort, uses a golf-like motion which rips what grass the blade makes contact with and arcs way over his head. The scythe is never lifted in either the draw or the return.