In 1975, Gary Dahl came up with a business idea that sounded like a joke.

Because it was one.

Dahl was a freelance advertising copywriter living in California when he was having drinks with friends one night. The conversation turned to pets and all the work that came with owning them. Dogs needed to be walked. Cats needed to be fed. Both could destroy furniture, get sick, and generate expensive vet bills.

Dahl joked that he didn't have any of those problems because his pet was a rock. The joke got a laugh. But Dahl kept thinking about it.

What if he actually sold rocks as pets?

Dahl sourced smooth stones from Mexico for pennies apiece and created the Pet Rock. The product itself was exactly what the name suggested: a rock. There was no manufacturing breakthrough and nothing particularly special about the stone.

What made the idea work was everything around it.

Each Pet Rock came inside a small cardboard box designed to resemble a pet carrier, complete with air holes and straw bedding. Dahl also wrote a 32-page owner's manual called The Care and Training of Your Pet Rock.

The manual explained how to properly care for your new companion and included instructions for teaching it tricks. "Stay" was particularly easy. "Roll over" required a little assistance. "Play dead" came naturally.

The whole thing sold for $3.95.

Dahl understood that nobody was really paying four bucks for a rock. They were buying the joke. And because the joke came neatly packaged in a box, it also made a perfect inexpensive gag gift.

The timing couldn't have been better.

Dahl introduced the Pet Rock in 1975, and the media quickly became fascinated by the ridiculous new product. Newspapers and television programs began covering the craze. Dahl appeared on The Tonight Show, giving the product even more national exposure.

By the Christmas shopping season, Pet Rocks were everywhere.

Department stores carried them. People gave them as gifts. More than a million Pet Rocks were reportedly sold during the fad, turning Dahl into a millionaire practically overnight.

Competitors quickly tried to get in on the action. Copycat rocks and other novelty "pets" began appearing, but there wasn't much anyone could do to protect the basic concept. After all, Dahl couldn't exactly patent the rock.

And almost as quickly as America became obsessed with Pet Rocks, it got tired of them. By early 1976, the craze was largely over.

Dahl tried other novelty products afterward, including a "Sand Breeding Kit" that allowed owners to supposedly breed male and female grains of sand. None came remotely close to the success of the Pet Rock.

But they didn't have to. Dahl had managed to turn a joke told over drinks into one of the most famous novelty products in American history. He took something anyone could find outside for free, spent pennies acquiring it, wrapped an entire personality around it, and convinced more than a million people to hand him money.

The Pet Rock lasted only a few months. Fifty years later, people still know what it is.

That's a pretty good sales job.