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In 1912, the Cracker Jack company made a fateful change to its business strategy. Starting in 1910, every box of the caramel-corn snack had contained a coupon, perhaps for a household appliance, or for a watch or a piece of jewelry. But Cracker Jack then decided to pivot hard toward selling to a different demographic, and began including a toy—perhaps a figurine, a toy car, or a toy ring—in every box. Sales exploded thanks to children’s sudden demand for Cracker Jack toys, and the subsequent boom in prizes included with children’s snacks and junk food has lasted for generations. (The McDonald’s Happy Meal toy, for instance, is a modern descendant.)

Surprise toys, whose specific characteristics are a mystery until after purchase, are the latest craze in the industry, and the revelation of what’s inside the packaging is part of the products’ appeal. L.O.L. Surprise Dolls, for example, which come in boxes that display only a vague silhouette of the doll inside, were named the 2019 Toy of the Year by the Toy Association, and a few years back, Hatchimals—toy creatures that hatch out of eggs—enjoyed a holiday demand rivaling that of Cabbage Patch Dolls and Tickle Me Elmo. Surprise toys can seem distinctly modern, given that their popularity is often linked to “unboxing” videos on YouTube. But when I asked Michelle Parnett-Dwyer, a curator at the Strong National Museum of Play in Rochester, New York, about this trend, she pointed out the popularity of Cracker Jack toys more than a century ago. While unboxing toys are certainly all the rage today, their central concept isn’t necessarily new. Their appeal isn’t limited to kids, either, but rather rooted in a natural human desire for relatively controlled suspense.

Many other “mystery” toys have enjoyed outrageous popularity over the past century. Baseball cards, for instance, saw their peak popularity in the ’80s, and Pokémon cards, first sold in the late ’90s, are still manufactured today. While Pokémon cards do lend themselves to a playable card game, they’re also popular collector’s items, as are baseball cards (and some Happy Meal toys and Cracker Jack prizes); part of the appeal is the possibility of acquiring a rare, valuable, or special addition to one’s stash.

The point of baseball cards in their heyday wasn’t necessarily “buying this baseball-card pack and playing a memory game, or anything like that. It would just be to see if you can get your favorite player,” Parnett-Dwyer said. “My cousin really was into it, and he had binders of all his baseball cards. He wouldn’t touch them—he would just neatly organize them, and then put them on the shelf.” Similarly, L.O.L. Surprise has quickly capitalized on mystery toys’ collectible potential: As Alana Semuels wrote last year for The Atlantic, a huge incentive for buying more L.O.L. Surprise Dolls is that you might unwrap “an ultra-rare.”

One reason surprise or mystery toys may seem more notable today is because they stand in contrast to a parallel trend in toys: customization. There are many toys now that you can select to your exact taste or likeness, Parnett-Dwyer said. American Girl dolls became fully customizable in 2017, encouraging many consumers to design dolls that look like themselves, and Mattel, the longtime manufacturer of Barbie dolls, recently launched a gender-neutral doll, “playing into the idea of making things that are relatable” to different types of kids. In other words, it’s become easier than ever to purchase a toy that is precisely what a child wants, and against that backdrop, the notion of a toy’s characteristics being a surprise at the time of purchase could be an exciting change of pace to a kid.

As for why these toys have such an enduring appeal, Parnett-Dwyer believes they hit a sweet spot between total predictability and total uncertainty; the former can bore kids, and the latter can upset or scare them. Mystery toys offer a kind of controlled surprise, a way to feel excitement and anticipation, but with a limited range of possible outcomes. “If you get surprised on, like, a ride, or in a movie, it can be scary,” Parnett-Dwyer said. “The beauty of these toys is that they’re not scary. There’s no nervous anticipation, because the surprise is only going to be fun. This eliminates all [the anxiety] but still gives you that same feeling of, Oh yeah, yes, I’m really excited.”

Sheila Williams Ridge, the director of the lab school at the University of Minnesota’s Institute of Child Development, agreed, and told me that the fun of unveiling something never gets old for kids. Throughout her career, Williams Ridge has worked with preschoolers and given them materials such as bins, small boxes, paper, and tape to experiment with at “sensory tables.” Frequently, she’s seen kids use the materials for “just wrapping stuff from around the room and giving it to each other.” In these exchanges, nobody wraps anything new or unfamiliar: “They just go wrap up a block and give it to someone else, and that someone else will excitedly unwrap it and be like, ‘Oh, thank you!’ Then the block goes back on the shelf.”

And sometimes just the process of unwrapping is the fun part—especially when that process requires a lot of problem-solving, trial and error, or interpersonal cooperation. What many kids enjoy about Hatchimals, for example, is the particular, nurturing way the hatching animal has to be coaxed out of its shell by its human caretaker.

That said, Williams Ridge pointed out, the act of unwrapping things never really gets old for anyone. It explains the popularity of the “unboxing” videos, certainly, but it also helps explain the popularity of subscription-based businesses, such as Birchbox for makeup and Carnivore Club for specialty meats. In subscription boxes like these, a curated selection of surprises arrives, and the consumer gets to experience the anticipation and then the unveiling. And in the age of Amazon, Williams Ridge noted, it’s not uncommon for adults to feel like the boxes that arrive at their doorstep—even if they’re only toilet paper or dog food—are somehow just a little more exciting than groceries.

And in some cases, surprise toys aimed at kids can even satisfy adults’ craving for mysteries of the fun-but-not-too-chaotic variety. Last year, Williams Ridge’s own daughters, 18 and 20 at the time, bought some mystery toys—Marvel-inspired kits that each required the buyer to chisel away with a little hammer to reveal one of five “gemstones.”

“The gemstones, they could’ve just gone to Michael’s and spent less, if it had just been the gems they wanted,” she told me. But Williams Ridge’s daughters had such a good time experimenting with how best to get the gems out of their packaging (“Maybe if we put warm water on it, this will happen faster”), this year, upon seeing the same toy for sale while out shopping, they remembered how much fun they’d had—and bought another one.

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