Foreshadowing in "The Lottery"

P. 264 "Bobby Martin had already stuffed his pockets full of stones, and the other boys soon followed his example, selecting the smoothest and roundest stones...made a great pile of stones."

This interesting seemingly insignificant snippet of the story is a hint of the cruelty to come. In reading this story through I glazed past this part. My thinking being: boys will be boys and boys play with rocks and throw them at each other. Also, I saw the "smoothest and roundest stones" and figured maybe these boys are stockpiling rocks to skip across some pond or lake to come. As the story focused around the gathering in the town center, the people gathering, the history of the lottery, and the lottery itself, I soon forgot about these stupid stones these boys had gathered. But at the end of the story, these stones make up part of the spectacle that is the lottery as they are hurled at Tessie Hutchinson. In reading through the early stones paragraph again, I picked up on the fact that these stones weren't being thrown immediately; they were being saved for something. If only I had known their cruel purpose, I would have been able to understand other subtitles of the story better. For example, the fact the box was black and the importance that EVERYONE from the town be there were details that make sense with the ending.