Revealing mistake: At the very end, a bat flying out of the mist toward the camera was intended to imply that Barnabas had taken bat form and could thus be around for a sequel. But through the haze, Barnabas can still be seen lying on the floor when the bat flies past. (01:36:25)
Revealing mistake: When Paul is carrying the dead body of Lucy from the lake her arm comes up to stop herself from falling.
Revealing mistake: When Miss Dempsey lifts up Gripper Burke and spins him around before throwing him out of the window, you can see that Bernard Bresslaw has been replaced by a dummy.