Early in the story what did Dill dare Jem to do?

Dill dared Jem to knock on the Radley's front door.

Jem said if Dill wanted to get himself killed, all he had to do was go up and knock on the front door. Our first raid came to pass only because Dill bet Jem The Gray Ghost against two Tom Swifts that Jem wouldn’t get any farther than the Radley gate. In all his life, Jem had never declined a dare.