One day, Scout's attention is attracted by one of the two live oaks standing at the edge of the Radley lot. She notices that there's a piece of tinfoil sticking out of the knothole of one of the trees. Upon further investigation, Scout discovers two pieces of chewing gum in the knothole, each one without its outer wrapper. It's not just any chewing gum, either, but Wrigley's Double-Mint.
Instead of shoving the gum into her mouth straight away, Scout waits until she reaches her front porch. Then, once she's satisfied that the gum looks and smells fresh, she starts chewing it.
Scout's excitement at finding two fresh pieces of gum is a perfectly normal reaction for a child of her age. However, she doesn't yet know the wider significance of her unusual find. In due course, she'll come to realize that the gum was left in the knothole of the tree by none other than Boo Radley.
This will turn out to be the first of a number of gifts left in the tree for the Finch children by Maycomb's resident boogie-man. In leaving the children these gifts, Boo is trying to establish a connection with a world from which he's been estranged for so long.
At this point, however, Scout doesn't realize this. She's just happy that she's managed to get her hands on some free chewing gum.