The Slinky may have become a phenomenon, but it was born an accident. Richard James, a naval engineer during World War II, was working with torsion springs when one fell out of a box; he watched in awe as it "walked" across a table. He spent the next few years tinkering with coils in search of the slinkiest shape—one that's fully compressed when relaxed. Shopkeepers thought it was too boring for kids used to loud and colorful toys, so James took the marketing into his own hands. He staged a department store demo that sparked a craze, and 72 years later, more than 300 million have been sold. Lots of reasons have been given for the Slinky’s enduring appeal: It's cheap, or it teaches kids physics. But Betty James, who came up with the name for her husband's famous offspring, always knew the secret, which she shared in a 2001 interview. "Children love simple things," she said. They’re not the only ones. | $6

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