How do jem and dill plan to send a note to boo radley?

Jem and Dill hatch a plan to leave a note for Boo in the Radley's window, using a fishing line. The note will ask him to come out sometimes and tell them what he's doing inside, and that they won't hurt him and will buy him ice cream. Dill says he wants Boo to come out and sit with them for a while, as it might make the man feel better.