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)
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.