For the millions of adults who grew up watching him on public television, Fred Rogers represents the most important human values: respect, compassion, kindness, integrity, humility. On Mister Rogers’ Neighborhood, the show that he created 50 years ago and starred in, he was the epitome of simple, natural ease.

But as I write in my forthcoming book, The Good Neighbor: The Life and Work of Fred Rogers, Rogers’s placidity belied the intense care he took in shaping each episode of his program. He insisted that every word, whether spoken by a person or a puppet, be scrutinized closely, because he knew that children—the preschool-age boys and girls who made up the core of his audience—tend to hear things literally.

As Arthur Greenwald, a former producer of the show, put it to me, “There were no accidents on Mister Rogers’ Neighborhood.” He took great pains not to mislead or confuse children, and his team of writers joked that his on-air manner of speaking amounted to a distinct language they called “Freddish.”

Fundamentally, Freddish anticipated the ways its listeners might misinterpret what was being said. For instance, Greenwald mentioned a scene in a hospital in which a nurse inflating a blood-pressure cuff originally said, “I’m going to blow this up.” Greenwald recalls: “Fred made us redub the line, saying, ‘I’m going to puff this up with some air,’ because ‘blow it up’ might sound like there’s an explosion, and he didn’t want the kids to cover their ears and miss what would happen next.”