The Brain Center at Whipple's - S5-E33
Continuity mistake: At the moment Chief Engineer Hanley turns off the projector, the lamps in the background come on at precisely the same moment. Mr. Whipple is standing in the middle of the room. No one else was in the room to turn the lights on.
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.