How did the author foreshadow that Johnny would use his knife in Chapter 2?

From the text:

I didn't think he'd ever get over it. Johnny never walked by himself after that. And Johnny, who was the most law-abiding of us, now carried in his back pocket a six-inch switchblade. He'd use it, too, if he ever got jumped again. They had scared him that much. He would kill the next person who jumped him. Nobody was ever going to beat him like that again. Not over his dead body...