What was in the knot -hole of one of the oak trees?

In "To Kill a Mockingbird" by Harper Lee, the knot-hole of one of the oak trees serves as a secretive communication spot between Boo Radley and the Finch children, Scout and Jem. The children find various items in the knot-hole, including two carved figures that resemble them, Chewing Gum, a spelling bee medal, and a pocket watch. These gifts symbolize Boo's kindness and desire for connection, as well as the children's growing understanding of him as a person rather than the mysterious figure they initially imagined. Eventually, the knot-hole is filled with cement by Boo's brother, symbolizing the end of that form of communication.