It was filled with cement from Mr. Radley.
Jem and Scout find a ball of twine in the knot hole the third time they visit.
Scout found two pieces of chewing gum minus their outer wrapper.
Scout first finds a piece of chewing gum - Wrigley's double mint, to be precise.
Boo Radley was the one who was leaving gifts for Jem and Scout in the knot hole of the oak tree.
They found some Indian-head pennies
Scout and Jem find two pieces of chewing gum, a ball of twine, and two Indian-head pennies in the knot hole of the tree. What frightens Scout is finding the gum and the twine, as they suspect someone has been leaving items for them in the tree, suggesting a hidden observer.
Nathan Radley puts cement in the knot hole to stop Boo Radley from leaving gifts for Jem and Scout. He believes that Boo's interactions with the children are inappropriate and wants to cut off their communication.
I can't think of all of them but one of them was gum and I think there was like a watch in it like a pocketwatch.
A stick of gum, indian-head pennies, pieces of soap carved to look like jem and scout.
The cemented hole in the tree represents Boo Radley's isolation from society. Nathan Radley fills the hole with cement to prevent Boo from communicating with Jem and Scout. Jem is heartbroken because he realizes the cruelty of this action.
Mr. Radley cements the knot hole shut.
As the tree grows, the knot hole can become covered up by new growth or get pushed out over time. The wood around the knot hole may also continue to grow and expand, filling in the space where the knot hole used to be.