A Hundred Yards over the Rim - S2-E23
Visible crew/equipment: When Christian walks up to the man in front of the diner, you can see a crew member in a plaid shirt and white pants reflected in the man's sunglasses.
Black Leather Jackets - S5-E18
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. (00:05:15)
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)
Mr. Garrity and the Graves - S5-E32
Deliberate mistake: Garrity blackmails the town citizens into paying him not to resurrect their unlamented "loved ones." Amazingly, every man in the saloon just happens to have hundreds of dollars ($500 - $1200 each) in his pocket to pay up with. In 1890 money, that's roughly equivalent to a group of modern-day bar patrons all carrying ten to thirty thousand dollars around in their pockets. The scenario was apparently used in spite of its incredibility just to more quickly advance the plot.
Revealing mistake: When Franklin leaves the check cashing window and walks to the right, a man with a pompadour haircut walks off screen left. In the next shot, with no time lapse, Franklin returns to his slot machine, and the same extra passes behind him from the right, once again exiting left. No way he could have moved that fast in the time allotted. (00:13:05)
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)
Visible crew/equipment: An equipment shadow moves across the back of Ellington's coat as Brother Jerome is telling him how the Devil was captured. (00:14:30)
Continuity mistake: Walter crumples the prescription slip and tosses it onto the bed - but in the next shot, it has disappeared. (00:05:15)
A Passage for Trumpet - S1-E32
Revealing mistake: Joey cannot see himself reflected in The Mirror. However when he walks past the booth, he has a clear reflection.
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)
Other mistake: Chambers asks what time it is on Earth, a strangely vague question to which the Kanamits grant an equally odd answer: on Earth, it is noon. It can't be noon everywhere on Earth at once. While it can be fancifully explained away ("They somehow knew to answer for the time zone he was taken from"), it still jars the viewer, because neither Chambers nor the aliens, both highly intelligent, should make this sort of imprecise mistake. Both director Richard Bare and Damon Knight, author of the original short story, confirmed this as a scriptwriting error that should have been caught before shooting began. (00:02:15)
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.
Death Ship - S4-E6
Visible crew/equipment: In the final shot of the ship ascending into space, one of the filament lines supporting the model is showing just above the saucer. (00:44:15)
In His Image - S4-E1
Revealing mistake: In the basement lab scene at the end, George Grizzard's double's face is visible in profile several times. (00:38:50)
Living Doll - S5-E6
Visible crew/equipment: The boom mike shadow is visible above Annabelle, after she tells Christie that Linda is at the door.
The Thirty-Fathom Grave - S4-E2
Factual error: On the bulkhead of the ship's sickbay is a standard 12-hour civilian clock. It shouldn't be there. All clocks aboard U.S. Navy vessels show 24-hour military time. (00:31:20)
Death Ship - S4-E6
Revealing mistake: When Mason puts the ID card back into the pocket of his dead duplicate, the "corpse" twitches its eyelids. (00:14:30)
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).
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.