The pendulum of the clock would not continue swinging while the clock was tipped back as it was being carried down the stairs.
The spirit leaves Forstmann's body while he is asleep and walks to the foot of his bed. The spirit is a transparent image of Sam, but the real body has transparent feet under the covers when seen in profile.
When Ed Wynn is breaking the window, the police car seen pulling up has a civilian license plate (GAE 246). Real police vehicles of the time have license plates with an "E" in a hexagon shaped outline and a series of numbers.
When he sees that his grandfather clock is running 10 minutes slow, Sam winds the clock but forgets to set the time.