Tribbles Old and New
Above: top: Kirk dresses down the shore leave party from the TOS episode The Trouble with Tribbles; bottom: same scene, but slightly altered, from Trials and Tribble-ations, a 1996 episode of DEEP SPACE NINE. Notice a couple of DS9 actors sandwiched in that line-up now. Image from the Ex Astris Scientia site.
12 years ago, STAR TREK DEEP SPACE NINE (1993-99) went back in time to STAR TREK THE ORIGINAL SERIES (1966-69) in its episode Trials and Tribble-ations. The DS9 cast, via computer graphics integration, woven into an episode with William Shatner, Leonard Nimoy and tribbles. Here's a behind the scenes documentary video from the DS9 DVD set:
Trials and Tribble-ations: Uniting Two Legends Part 1
Trials and Tribble-ations: Uniting Two Legends Part 2