Continuity mistake: Becker is standing on the porch at "Block 6" and there are no handrails. When we return to Becker he is in the center of the square area and in the background handrails are there. (00:07:55)
Continuity mistake: Block 6 looks to have a no cardboard over the window beside the "Block 6" sign. Then later on they have cardboard there. (00:12:20 - 00:14:55)
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)
Continuity mistake: When the contractor forces his way into Wanda's apartment, she faints, her head landing in the center of the bare floor. But in the following shot, as the contractor leans over her, Wanda's head is at the edge of a large throw rug. (00:15:30)
Continuity mistake: After sounding the "alert" for his guests, Raden turns around to fully face them, and as he addresses the Reverend, from the back his hand is gripping the arm of the chair. In the the next moment, there is a frontal shot, and Raden's hands are folded on his lap.
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)
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)
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)
The Last Rites of Jeff Myrtlebank - S3-E23
Continuity mistake: An entire piece of toast disappears off of Pa's plate from one shot to the next. (00:08:40)
The Last Rites of Jeff Myrtlebank - S3-E23
Continuity mistake: Jeff corners Orgram behind a tree with a tire swing hanging from it and punches him to the ground. But in the next shot, Orgram is still on the ground and the tree and tire swing are nowhere in sight. (00:17:35)
Continuity mistake: During Rod Serling's opening narration you can see over his shoulder part of the outline of the portal to the 4th dimension, which would be drawn there later in the story.
Continuity mistake: The hundreds of ropes used by the tiny people to pull down Craig's statue vanish in the next shot, when the statue hits the ground. (00:23:55)
Continuity mistake: When the decrepit Mr. Holt gets his new young body (briefly necessitating a different actor in the role), his German accent mysteriously disappears. He gets it back when he returns to his old body. (00:21:00)
Continuity mistake: When we first see it, the grandfather clock is stopped at 2:33. But when Alex opens the case to adjust and restart it, the clock reads 4:40, and he moves the hands to 2:33 after checking his watch. (00:01:05 - 00:03:50)
I Sing the Body Electric - S3-E35
Continuity mistake: When Tom races into the house, the exterior shot is of a front door with six window panels. But when we cut to the interior view of him coming inside, the door has suddenly become solid, with no windows at all. (00:13:20)
The Changing of the Guard - S3-E37
Continuity mistake: While at the window listening to the Christmas Carolers, the eyeglasses Professor Fowler is wearing disappear and reappear, depending on the camera angle.
Continuity mistake: As Ilse walks toward the front of the classroom, she passes the kids in the last row and is even with the kids in the next-to-last row, but in the following shot, shown from her point of view, she's passing the kids in the last row again. (00:30:45)
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. Ferguson is measuring the wax figures, he's shown holding a tape measure up against the figure of Landru (the one holding the rope). In the next shot, the figure is shown with no one near it. The next shot again shows Mr. Ferguson measuring the figure. (00:45:35)
Passage on the Lady Anne - S4-E17
Continuity mistake: During their conversation over tea, Mr. McKenzie tells the Ransomes about the other people aboard ship. One elderly couple, the Whiteaways, are sitting in the background in almost complete shadow - until McKenzie introduces them. Then we see them in sudden brilliant light, and they've shifted their seating positions relative to the table. When we cut back to the master shot, they're back in shadow and back in their original positions. (00:29:55)
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.