Continuity mistake: When he introduces himself to Millicent inside the train station, Paul is wearing a dripping wet raincoat. It stays wet in the close-ups, but in the next several inter-cut two-shots, it's completely dry. (00:11:15)
Continuity mistake: In the final scene, the position of the silver dollar lying next to Franklin's hand changes several times between shots. (00:23:45)
Continuity mistake: Renard gets his bottom wet from sitting down and tying his laces on his new shoes. But after he is hit by the car, his trousers are dry.
Continuity mistake: When Nan first swerves to avoid The Hitch-Hiker, her 1959 Mercury briefly turns into a 1957 Ford. It also changes from a light to a dark color. (00:17:15)
The Lonely - S1-E7
Continuity mistake: Allenby brings Corey a stack of paperback books. He's holding them with the back covers facing out until the shot cuts, and then the stack of books has reversed itself in his hand: the back covers are now facing inward. (00:20:30)
Continuity mistake: Henry closes the door of the rabbit hutch, but it bounces back open. When he turns back to the hutch a minute later, though, the door has closed itself. (00:16:30)
Stopover in a Quiet Town - S5-E30
Continuity mistake: Bob's cigarette sets the artificial grass on fire, and he rapidly stamps it out. When he finishes extinguishing the flames, the grass is scorched, but intact. He doesn't touch it again, but one shot later, the burned grass and all its ashes have vanished and a huge hole has appeared, revealing the metal mesh underneath. (00:13:50)
A Short Drink from a Certain Fountain - S5-E11
Continuity mistake: When Raymond arrives to check on Harmon, Flora is sitting at the breakfast bar opening the morning paper. She's holding it straight up in front of her, but when the shot reverses angles, the paper is suddenly lying flat on the bar. (00:16:15)
Showdown with Rance McGrew - S3-E20
Continuity mistake: Rance McGrew's white horse is tied up with its head just a few inches from the hitching rail, but a moment later is untied and several feet away from the rail. Next shot, it's tied up close again, though no one's touched it. Finally, it's completely loose, and at the episode's end, is wandering into the street. (00:22:00 - 00:23:30)
Continuity mistake: No one drinks much lemonade, so there's neither time nor need for Eve to refill the pitcher during the brief cut to a scene on the porch. Yet after she has emptied its contents into the glasses on the tray, the lemonade pitcher refills itself. (00:15:15 - 00:19:10)
Continuity mistake: As the hour is striking midnight, Maggie's toy robot turns itself on and walks past the alarm clock on her bureau. After a cut to Lou and Mr. Death, the scene returns to Maggie's room, and the robot walks past the clock again. (00:22:00)
Continuity mistake: After Franklin falls through the window at the end, he lands on the pavement below - on top of the broken window frame. Next shot, when the police are examining the body, the window frame has moved out from under Franklin and is lying about a foot away. One shot later, though, it's back in its original position underneath him. (00:20:00)
Continuity mistake: Hall leaps through the plate glass window. In the interior shot, he breaks the glass and is 3/4 of the way through the opening (up to his knees) - until we cut to a view from outside the window. Then he's just crashing through at shoulder level. (00:22:45)
Continuity mistake: Walter crumples the prescription slip and tosses it onto the bed - but in the next shot, it has disappeared. (00:05:15)
Showdown with Rance McGrew - S3-E20
Continuity mistake: The saloon's windows are much narrower inside than they are on the outside. (00:17:20)
Continuity mistake: When Jackie leaves the office, the clock reads 10:12. The ensuing continuous scene with Winter and Mr. Smith is almost 6 1/2 minutes long, yet at its end, the same clock has advanced only 2 minutes, now reading 10:14. (00:33:00 - 00:39:15)
Continuity mistake: When Mr. Bookman is leaving his apartment to get away from Death, there is a note tacked to the door that is about level with his head. In the next shot, he's out in the hallway locking his door and the note has moved up to about 6 inches above his head. (00:12:35)
Continuity mistake: The events shown are supposed to take place at almost exactly midnight, yet when Conny goes to the graveyard the sky is bright and everything is well lit, much brighter than moonlight. Just as he enters the graveyard there is an abrupt change in lighting and the scene is suddenly much darker.
Showdown with Rance McGrew - S3-E20
Continuity mistake: The car Rance drives onto the set can be seen in the street from inside the saloon, but disappears when Rance, in character, comes through the swinging doors. It's visible again in the very next shot, but vanishes anew when Jesse James comes through the doors, after which it yet again reappears in the very next shot. (00:04:30 - 00:07:20)
Continuity mistake: During the birthday party scene, as the close-ups and master shot are intercut, Anthony's hair changes back and forth from being combed straight forward to parted on the left and combed to the side. (00:15:10)
Answer: It's explained in the episode. The aliens are experimenting to see how humans react to various scenarios. This just happens to involve them using super strength.
Thanks. It's been a long time since I saw the episode so I forgot.