Sunny Park smelled like warm grass and bubblegum ice cream. The sun made the pond sparkle, and the ducks made wobbly Vs as they glided across the water. Lila and Sam were busy building a leaf boat with a tiny stick flag that said, "S.S. Giggle." "The wind is perfect," Lila said, squinting one eye like a sea captain. "Set sail!" "Aye-aye!" Sam saluted with the stick. The boat made a brave little bob, then bumped back to shore like a shy turtle. That was when Lila noticed it. Next to the bench with the gum-stuck corner and the peely paint, a small metal box was bolted to the lamppost. It was about the size of a lunchbox, shiny enough to see your nose in, and right in the middle sat a big yellow button. Sam leaned close. "What do those tiny words say?" Lila wiped the dust with her sleeve and read, slowly and carefully, "Giggle Button. Press only if you love laughing." They looked at each other. They looked at the button. Then they both squeaked the kind of squeak you make when you spot a puppy wearing sunglasses. "What if it makes the ducks tell jokes?" Lila whispered. "What if it makes the grass tickle our toes?" Sam whispered back. "What if it makes the sky do a cartwheel?" "What if it makes our noses beep?" Sam poked his own, just to check. Beep. No beep. Mr. Pockets, the park keeper, trundled by with his squeaky cart. He wore a green cap and about a hundred pockets. Every pocket had a thing: a tiny rake, a stack of tickets, a yo-yo, a sandwich, three pinecones, and one polite frog that said, "Ribbit," as if it were holding a door for someone. "Mr. Pockets!" Lila called. "Have you seen this before?" Mr. Pockets peered at the box through his glasses and then through a second pair he pulled from another pocket. "Hm! Never seen that before. Looks official. Looks shiny. Looks like it would smell like lemons if I sniffed it. But I won't sniff it, because last time I sniffed a thing, I sneezed confetti for two days." "Should we press it?" Sam asked. Mr. Pockets tugged his cap, thinking. "My advice? Read the sign, count to three, and make sure nobody is standing on a banana peel." He pushed his cart onward, and the polite frog said, "Ribbit, after you," to a squirrel. A squirrel with a magnificent tail scampered down the lamppost and patted the button with tiny paws. Pat. Pat. It blinked a shy little blink, like a firefly learning how. "It blinked!" Lila squealed. "Maybe it's waiting for a proper press," Sam said. "Like when Grandpa's doorbell doesn't work unless you press it with your elbow." A duck waddled over, tilting its head left, then right. "Quack?" it asked, which meant, "Is this snack-related?" "It might be laugh-related," Lila told the duck. "Which is almost as good." Sam rolled up his sleeves. "Okay. We need a plan. Step one: safety." He pointed at the ground with his stick. "No standing on banana peels. Check." Lila checked. No bananas. Just a suspicious leaf that looked like a banana pretending to be a leaf. "Step two: science. We'll try a gentle test press." Sam plucked a long blade of grass. He tickled the button with the tip. The button made a sound that was not quite a beep and not quite a hiccup. Beepcup. The grass gave a tiny snort, like a giggle it wasn't supposed to have. Lila stared. "Did the grass just laugh?" "Impossible," Sam said. Then the grass laughed again, a soft hee-hee that made the blade wobble. Lila and Sam looked at each other with eyes as big as cookies. "Step three: proper press," Lila said, feeling brave and fizzy. "But we need to be ready." They set their leaf boat on the bench, just in case it needed to float away from too much silliness. Lila tied her hair into two very serious puffs. Sam tightened the Velcro on his shoes with a chhhrrrip. They both took a step back, then a step forward, then a step sideways because the duck had parked itself exactly where their toes wanted to be. "All right," Sam said. "We'll press it together. On three." The squirrel saluted. The duck blinked. The frog, from across the path, called softly, as if it were a librarian, "Ribbit." "One," said Lila. A tiny breeze tiptoed by and wiggled the leaves. "Two," said Sam. The fountain in the pond bubbled a little slower, like it was listening. "Thr-" Lila began, but the button pulsed warmly under her fingertip, once, twice, like a sleepy heartbeat. They both froze. The yellow circle glowed a little brighter. A very faint humming started, the kind that tickles your ears and makes you want to giggle for absolutely no reason at all. Mr. Pockets paused at the top of the path and took off his hat. The wind stopped fussing with the trees. Even the clouds seemed to lean closer, the way you lean closer when someone is about to tell the best, silliest joke. Lila swallowed her fizz. "Okay. On three for real." "One," Sam whispered. The button hummed. "Two," Lila whispered. The duck scooted one inch closer. "Three!" they both whispered. They pressed. The button gave a bright, happy blink. The lamppost made a tiny throat-clearing sound-"ahem"-as if it were getting ready to speak. The bench under their leaf boat shivered like a cat stretching. The humming turned into a tune that sounded almost like a laugh trying to hold itself in, and then the button said-"HIC!" and-