In Chapter 7 of To Kill a Mockingbird, what have Jem and Scout found in the knothole?

In Chapter 7, Jem and Scout find several items in the knot-hole of the Radley tree. The first item they find is a ball of twine. At first, the children think one of their classmates is using the knot-hole as a hiding place. Later on, Jem and Scout find two small images carved out of soap. The figures resemble Scout and Jem, and the children begin to wonder who made them. In the following weeks, the children find a whole pack of chewing gum and a tarnished spelling bee medal. Four days after finding the medal, Jem and Scout find a pocket watch on a chain with an aluminum knife. Scout and Jem decide to write a thank you letter to the person who is leaving gifts for them in the knot-hole. On the day Jem attempts to leave the thank you letter in the knot-hole, he finds out that it has been filled in with cement. Jem and Scout are both devasted. Jem asks Nathan Radley why he filled the knot-hole with cement. Nathan claims that the tree was dying, but in reality, he just wanted to stop Boo from communicating with the children.