1967
The Trouble with Tribbles (Star Trek)
The Starship Enterprise docks to a base where a businessman is selling small creatures called Tribbles. They reproduce quickly and soon fill both the ship and consume the grain stores of the station.
1967
Mirror, Mirror (Star Trek)
Crew members from the starship Enterprise acidentally teleport into a parallel ("mirror") universe populated by evil copies of their ship and crewmates.
1988
Datalore (Star Trek: The Next Generation)
The android Data, along with the crew of *Enterprise*, return to the planet where he was found and discover an identical-looking android.
