The Mirror - S3-E6
Visible crew/equipment: Clemente walks over to the portrait of the former ruler, and throws his glass. Just as he completes the action, the camera looks at the portrait. There is a movement of what appears to be a device on the right side of the shot firing the glass.
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.