What events have reawakened the interest in Scout and Jem in the Radley place even before Dill returns from his second summer in Maycomb?

Scout notices a shadow on her curtains and believes someone is watching her. Jem finds his pants mended and neatly folded on the Radley fence. Someone leaves gifts in a knothole of the Radley tree, such as gum, a ball of twine, and soap carvings. These mysterious occurrences spark their curiOSity about the Radley place.