Lost in Space was well into its third and final season of production and Jonathan Harris, who played the conniving centerpiece of the show, Dr. Smith, was relaxing in his dressing room. There was a rap on his door. Peter Packer, one of the lead writers on the series and a close friend of Harris, poked his head in. Packer shamefully shuffled into the dressing room, holding something behind his back.

"What you got there?" Harris asked. The actor considered Packer to be the best writer working for Lost in Space.

"You won't like it," Packer said.

"Let me make the decision," Harris said. "What have you got there?"

Packer handed over a script. The front page read, "The Great Vegetable Rebellion." Harris found the title amusing and told his friend as much.

"You'll change your mind," Packer said.

In the last half-century since "The Great Vegetable Rebellion" originally aired, people have indeed changed their mind about the penultimate episode of Lost in Space. When TV Guide printed its 100 Greatest Episodes of All Time in the summer of 1997, "The Great Vegetable Rebellion" ranked at No. 76 — five spots above Maverick's brilliant "Shady Deal at Sunny Acres" and 16 spots above Star Trek's tragic-romantic classic "The City on the Edge of Forever." So, at some point, what is considered to be Lost in Space's weakest episode was held in higher esteem than what many consider Star Trek's greatest hour. At least in some critic's eyes.

The cast and crew of Lost in Space certainly did not hold the same opinion of the material. 

Mark Goddard stifles a smile.

Guy Williams and June Lockhart, the stars who played John and Maureen Robinson on the show, laughed throughout the filming of the episode. They couldn't even hide it from the camera. Williams stands snickering in several shots, averting his eyes from guest star Stanley Adams, who pranced around the fake foliage in a giant orange foam carrot costume. Mark Goddard, who played Major Don West, also seems to fight every urge to not break into laughter.

Penny dozes through most of the episode.

Angela Cartwright, a.k.a. Penny Robinson, is napping throughout the entire tale. For their insolent behavior, Williams and Lockhart were written out off the next two episode in production, "Fugitives in Space" and "Space Beauty," if you're wondering why their characters went missing.

Harris took the script home and read it that day Packer first delivered it. "It was a disaster," he said. Packer apologized to series creator and producer Irwin Allen. "I'm sorry," the writer said. "Do we have to do this one?" Allen blurted, "Sure, why not?" Packer confessed, "I've written myself out. I don't have another idea in my head."

Well, we respectfully disagree. Packer had ideas. A planet populated by sentient plants is an idea. A birthday party for a robot is an idea. Vines crying out in pain like electronic piccolos is an idea. A hippie with purple hair and lettuce heart is an idea. A giant fern attacking Will and Judy is an idea. Dr. Smith transmutating into a massive celery stalk is an idea. An eight-foot, anthropomorphic carrot clutching at his breast and crying "Moisture! Moisture!" before splashing water over his torso from a gas pump — that's an idea!

They are wacky, whimsical ideas, sure, but they are ideas. And we are here to defend them.

Moisture! Sweet moisture!

Would you nitpick the finer plot details of Scooby Doo, Where Are You! Would you question the scientific basis behind giant mutated turtles who skateboard and scarf pizza in the sewers? Did you click away from Grape Ape because gorillas are not really 40-feet-tall and purple in nature? No. Those were cartoons, for children. And by its third season, Lost in Space had evolved from a black-and-white sci-fi series inspired by 1950s cinema into a live-action cartoon. Following the colorful bootsteps of Batman, Lost in Space was camp. By the end of its run, Lost in Space was following the muse of The Jetsons, not Star Trek. (Though, Star Trek would go through similar changes in its third season, as demonstrated best by "Spock's Brain.")

Look at "The Great Vegetable Rebellion" as animation — and it has that same bright, bold, simple colors of animation — and it delights. So what if the controls for the steam mechanism is conveniently located directly beneath the Robinson's prison cell, and easily accessible by hatch? Is it any sillier than Cobra Commander installing a fat, red "SELF DESTRUCT" button in his secret base for his nemesis G.I. Joe to readily press?

We want this cake on our birthday.

The episode begins aboard the Jupiter 2 and sets the comical tone. The Robinsons are celebrating the "birthday" of the Robot. They even managed to find party decorations and silly hats stashed somewhere in the spacecraft. John Robinson sports a little sombrero. Maureen has baked a cake for a robot — who, we want to reiterate, is a robot that can not consume cake — and its even decorated with a model of B-9 made of frosting. The Robot wears wear a golden crown like he's at Burger King. How could that not make you smile? We're not going to deeply analyze the plot as some extended metaphor for getting children to eat healthily or a thinly veiled treatise on environmentalism. It's simply old-fashioned, sugary fun, something to pair with a bowl of Quisp on a Saturday morning.

While Williams, Lockhart and Cartwright visibly aired their contempt for the material, Harris and Adams leaned into the script with Shakespearean relish and chewed up the scenery like it was ants on a log for an after-school snack. James Millhollin, who played the purple-haired "Willoughby the Llama," was best known for stuffy bureaucratic types. He seemed to genuinely enjoy stepping out of his pigeonhole of befuddled middle-management to portray a crunchy hippie. Seeing professionals like Williams and Lockhart break is amusing, too. It humanizes them. In hindsight, it's a fascinating peek into the behind-the-scenes dynamics of the show.

Judy and Will face an angry fern.

For true connoisseurs of Lost in Space, "The Great Vegetable Rebellion" gave Judy Robinson (Marta Kristen) her time to shine. In the hierarchy of Robinson adventures, Judy was often the forgotten third child, well behind Will, the true protagonist of the show, and the younger Penny. Judy uses her wits to rescue Dr. Smith. She wields a machete. She faces off against that giant fern (okay, with Will in that scene, but still).

And, when a few of her co-stars were written out of future episodes for insubordination, Kristen continued to get the spotlight in the subsequent script "Space Beauty." (Though it was filmed after "Vegetable Rebellion," it aired earlier in the third season.) For Judy fans, this was her prime.

More than anything, "The Great Vegetable Rebellion" sticks in the memory. You remember where you were when you first saw it. We bet, at the time, as a child, you found it enchanting. And it can still bring you back to that mindset if you allow it.