Deliberate mistake: Sport's voice is noticeably dubbed by a different actor in several scenes throughout the episode. Her voice inside Aunt T's house is the original audio track done by the child actor. During the other scenes, the voice is done by June Foray (uncredited).
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)
Living Doll - S5-E6
Continuity mistake: When Erich falls downstairs, Talky Tina flies off of the stairs too, yet in the next shot she's shown still rolling downstairs. (00:23:25)
Living Doll - S5-E6
Continuity mistake: When Erich throws Talky Tina across the room, when she hits the floor, her arms and hair change position between shots.
Revealing mistake: As Connie approaches the graveyard the sky in the background is obviously a painted backdrop, as there is a visible seam.
The Trouble with Templeton - S2-E9
Continuity mistake: When Booth grabs her, Laura's long string of beads breaks. When she starts dancing a moment later, though, they've somehow repaired themselves. (00:18:50)
An Occurrence at Owl Creek Bridge - S5-E22
Continuity mistake: After crawling from the water onto the shore, the Southerner lies on his back with his shirt gaping open, exposing his entire chest. But in the next shot, his shirt has fastened itself, completely covering his chest again. (00:16:00)
The Jungle - S3-E12
Continuity mistake: Richards opens the door and finds a lion on the bed over his wife's body. When the door first opens, the corpse has dark hair and the blanket is twisted and disarrayed. But when the shot cuts to the lion leaping, the corpse's hair is a lighter color and the blanket is neatly spread across the bed. (00:23:40)
Visible crew/equipment: When Sykes opens the Sheriff's office door to leave, the "sky" outside has a very large equipment shadow on it, hanging over the building across the street. (00:05:10)
Continuity mistake: When Ferris is in the phone booth, he tries to get the operator but then hangs up the phone. He then scans the Town Square. The camera pans counter-clockwise and the receiver is nowhere in sight.
The Incredible World of Horace Ford - S4-E15
Factual error: In the opening scene, Horace painstakingly loads his six-shooter cap pistol with a six-cap round - then shoots his boss with it seven times. (00:00:40)
Audio problem: The keys we see being depressed on the player piano never bear any resemblance to the actual notes we hear. (00:13:00)
Continuity mistake: When the Union soldier arrives on the horse, Lavinia points a shotgun at him, holding it at chest level. But when the shot cuts, she suddenly has it up to her cheek. (00:15:00)
The Lateness of the Hour - S2-E8
Visible crew/equipment: As Robert is pouring Dr. Loren's drink, an equipment shadow moves across the top of Jana's head in the foreground. (00:08:20)
The Lateness of the Hour - S2-E8
Visible crew/equipment: When Jana is screaming "No pain!" at the top of the stairs, a film crew member's shadow can be seen moving on the wall behind her. (00:22:30)
King Nine Will Not Return - S2-E1
Continuity mistake: Embry soaks the front of his shirt with water from the canteen. But when he runs toward the B-52's cockpit and turns around a moment later, his shirt is completely dry again. (00:10:10)
Deliberate mistake: The signs at Dachau Concentration Camp are in English.
Death Ship - S4-E6
Visible crew/equipment: Just after the ship re-attains orbit, the shadow of a production crew member moving his arm can be seen on the wall at the upper right of the shot. (00:38:30)
Probe 7 - Over and Out - S5-E9
Factual error: Cook draws his sun and planets in the sand, saying that it's "my galaxy." When Norda draws hers, he calls it another galaxy. Wrong. He's drawn a solar system, not a galaxy. (A galaxy is a collection of millions of solar systems.) The terms are in no way synonymous - there's a vast difference, and a trained astronaut would definitely know that. Their little ships can't possibly cross galactic voids (that would require tens of thousands of years, even at many times the speed of light), so Cook and Norda's planets are in different star systems in the same galaxy - this one. (00:16:30)
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.