Revealing mistake: We see Redfield's car strike the invisible barrier from a side angle. It jerks to a stop and the hood flies up, but there's no other front end damage - until the angle shifts to a forward view, a shot of an identical car that had been previously wrecked. Now there's suddenly considerable damage to the front end, and the hood is in a different, much more crumpled position. (00:11:10)
Revealing mistake: Throughout the episode, the "frozen" people can be seen breathing and moving slightly. This is particularly apparent in the beauty contest tableau.
Revealing mistake: When Hall races toward the window to jump, the stunt man is just a little too apparent as he leaps, primarily due to a very bad wig. (00:22:40)
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)
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)
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.
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)
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)
Revealing mistake: As Connie approaches the graveyard the sky in the background is obviously a painted backdrop, as there is a visible seam.
A Most Unusual Camera - S2-E10
Revealing mistake: The crooks in this episode appear to have obtained the same pile of funny money that the Castles received in "Man in the Bottle." The bills don't even vaguely resemble any real U.S. currency. (00:20:25)
Revealing mistake: The strings on the guitar are extremely loose. While they would make a sound, it wouldn't be anywhere near the proper sound. The guitar sound throughout the episode doesn't match up to the strokes of the guitar either.
Revealing mistake: The woman leads a simple but hard life, however, in several close ups, she has long, tapered, finely manicured and polished fingernails.
Revealing mistake: In the window there are already broken areas where the glass gets broken when Captain hits it. On the bottom pane the grill on the top, bottom and right have a crack before the Captain even hits it. (00:19:00)
Revealing mistake: When Lanser goes below deck frantically trying to find people and tell them to leave the ship, when he opens the door at end of the corridor, it's a bit too obvious that the hallway behind that door is nothing more then just a painting.
Revealing mistake: When all of the neighborhood children push Bevis's car for him, one of them looks directly into the camera.
A Nice Place to Visit - S1-E28
Revealing mistake: When Valentine tries to shoot Pip, he shoots the lamp to see if his gun works. The lamp breaks a full second after he shoots it. It was obviously done by special effects.
A Thing About Machines - S2-E4
Revealing mistake: When the electric razor is coming down the stairs after Finchley, the wire used to pull it is visible. (00:19:50)
Revealing mistake: Stock footage used here is far too obviously borrowed from several old movies. While the episode is set in the 60s, people's clothing and all the cars are noticeably many years out of date. (00:03:05)
Revealing mistake: Many of the "frozen" Union soldiers can be seen blinking, breathing and wavering in place amidst their regiment. (00:07:30)
Revealing mistake: Mr. & Mrs. Castle wish for a million dollars in 5 and 10 dollar bills. But the bills they receive all have the same pattern printed on both sides, a pattern which which doesn't resemble any real US currency. There's also not nearly enough of the bills to total a million dollars. (00:12:30)
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.