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)
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.