For big fans of The Waltons, watching for Grandpa’s improvised moments provides some of the greatest joy in rewatching episodes.

Sometimes these improvisations would catch his cast mates off-guard, but that was no matter for Grandpa actor Will Geer, who as a young man learned improvisation from one of the first celebrity actresses, Minnie Maddern Fiske.

For example, in the two-part episode called "The Wedding," there’s a moment you can catch where John-Boy and Grandpa have an exchange at dinner.

In the scene, Grandpa tells John-Boy, “Into each life, some rain must fall, so wear your smile for an umbrella.”

If you watch, you’ll see Thomas laugh and say, "Who wrote that?"

Geer told The Boston Globe in 1974 that at minimum a quarter of his dialog is totally improvised.

"I have great leeway in my dialog," Geer said. "I’m allowed to improvise at least 25 percent of the lines."

On top of being talented as a veteran improvisational actor, Geer also had the gift to improvise as Grandpa because he felt as if he and Grandpa were the exact same person.

That means, basically, every improvised line was just Geer being Geer and saying the kind of thing he would say to his real grandchildren.

"It’s the easiest job I ever had,” Geer said. “I’m just playing myself. Like Grandpa Walton, I’m a father (of eight) and a grandfather (of three). I share his fondness for the open air. I’m an ecologist. I’m great on seeds and planting."

Because Geer and Grandpa were so closely aligned, writers didn’t even bother to give Grandpa lines in many scenes.

"‘Just say it the way you want to, gramps,’ they tell me," Geer said. "‘You’ve lived it all. By now, you know this character inside out.’"

If you want to geek out over all of Geer’s hilarious and charming improvisations, you might want to check out this thread on a Waltons fan page cataloging "Grandpa’s impromptus."

Fans recollect everything from Grandpa squeezing a tomato onto Jim Bob’s face to the way he interjected with "A-men and A-women."

They also recalled how Eric Scott remembered the whole cast struggling to keep up with what Geer would say next.

You could definitely say Geer spiced up the show.

When Geer was first offered the part of Grandpa, he wasn’t sure if the show had enough legs to keep an audience coming back week after week.

"When it started, I thought it was too syrupy and sweet," Geer said. "‘This is fine for Christmas, once a year, but every week? I don’t know,’ I said to myself."

That impression quickly changed when the show became popular.

"I learned kids need Christmas every week," Geer said. "I was impressed with the way the series caught hold and the quality fare it provided. It had the warmth and glow of folklore, which, in a sense it is. I’m proud of being part of it."

That gave Geer an excuse to continue his improvisations on The Waltons until he passed away in 1978.

We can be sure Geer would’ve been glad the show stretched on for three more years after the tragic loss of Grandpa.

"The Waltons can go as long as it wants, as far as I’m concerned," Geer said.