[语言求助] collapse in on himself

A few months earlier, when crisp leaves had begun slipping to the ground, signaling the end of summer, Dad had been in high spirits. His feet tapped show tunes at breakfast, and during dinner he often pointed at the mountain, his eyes shining, and described where he would lay the pipes to bring water down to the house. Dad promised that when the first snow fell, he’d build the biggest snowball in the state of Idaho. What he’d do, he said, was hike to the mountain base and gather a small, insignificant ball of snow, then roll it down the hillside, watching it triple in size each time it raced over a hillock or down a ravine. By the time it reached the house, which was atop the last hill before the valley, it’d be big as Grandpa’s barn and people on the highway would stare up at it, amazed. We just needed the right snow. Thick, sticky flakes. After every snowfall, we brought handfuls to him and watched him rub the flakes between his fingers. That snow was too fine. This, too wet. After Christmas, he said. That’s when you get the real snow.