As soon as that ep aired, my friend Frank, who was an editor and commercial producer at a cable station at the time, called me up, dying to try it himself. A bunch of us gathered at his studio to try that trick, and it turned out to be pretty easy, electronically. The actor puts the glass down, the tape is rolled back, the actor moves to the other side, the video split screen edge is moved over with a simple dial, and the actor picks it up from the other side. It only took a few minutes to get it right. I may even still have a copy on VHS somewhere!It was already an old technique by that point. I used to think that TNG: "Datalore" was innovative in doing a split-screen shot of Lore putting a glass down and Data picking it up (or was it vice-versa?), but since then I've seen similar "interactive" split screen shots done in 1940s-50s productions.

