Dots of Flour

Simon was confused. He kept finding dots of flour. They were on the street and under trees, all the way to school.
“Maybe someone had a bag of flour, and it leaked,” said his friend Jim.
“Maybe it’s not flour at all. Maybe it’s space dust from aliens,” said his friend Grace.
But they were both wrong. After school, Simon followed the dots of flour to a park. There was a big X made out of flour by a table. “Weird,” said Simon to himself.
Just then, a group of people ran up. They wore shorts and T-shirts. “We’re playing a game,” they said to Simon. “One runner marks a trail with dots of flour. The rest of us run around and try to find the trail. It’s a game!”
“It’s strange,” thought Simon as he walked home. But he was glad he had solved the mystery.