In television’s early years, most comedies were filmed in front of live studio audiences. The problem was that sometimes the jokes fell flat, or scenes had to be re-shot. On screen, the silences felt awkward. Producers worried viewers at home would think the shows were not funny.

A CBS sound engineer named Charles “Charley” Douglass came up with a solution in the 1950s. He invented the “Laff Box,” a suitcase-sized device loaded with recordings of real audience laughter. By pressing different keys, he could add chuckles, giggles, or roars of laughter exactly where they were needed.

For decades, Douglass guarded his invention closely and even traveled with it to sweeten shows himself. From I Love Lucy to The Brady Bunch, much of television comedy was powered by his hidden laugh machine. And while many modern comedies no longer rely on canned laughter, some shows, such as The Big Bang Theory and Mom, have continued to use it.