Revealing mistake: The aliens cause a power fluctuation, and Mr. Tillman complains that all the lights in his house are flickering on and off. But the lamps in his living room are burning steadily. The "flickering" light is originating from what is obviously stage lighting above the set.
Revealing mistake: When the town's people are waiting for Garrity's arrival at midnight, we hear an old clock informing everybody it is midnight and they all turn around to see. But look at the time on the clock - you can quite clearly see that it is actually five minutes till 6 o'clock.