On Thursday We Leave For Home - S4-E16
Visible crew/equipment: As the men talk in the cave, the boom mic is plainly visible.
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)
Death Ship - S4-E6
Visible crew/equipment: Just after the ship re-attains orbit, the shadow of a production crew member moving his arm can be seen on the wall at the upper right of the shot. (00:38:30)
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.