At the beginning of this incident in the novel, Dill dares Jem to take action to bring Boo Radley out of his house, to force him into the open so that the children can confront Boo and change his way of thinking. In other words, Dill wants to address the nature of Boo's "problems" through direct action. Jem respects the principle of "the dare," but he considers Dill's proposal to be a suicide mission. Jem can't refuse the dare, however, so he tries to reason with Dill to make him see the error in his thinking. This "negotiation" goes on for a while until Dill backs off a bit and makes a counter offer. Jem will not have refused the original dare if he now agrees to go into the Radley yard and slap the side of the house. Jem is suspicious of Dill's new offer, looking for deceptive loop holes in it, but when Dill assures him it is an honest offer, Jem accepts. He then assesses the Radley property, deciding how best to fulfill the dare without loss of life:
[Jem] walked to the corner of the lot, then back again, studying the simple terrain as if deciding how best to effect an entry, frowning and scratching his head.
When Scout openly scoffs at her brother, however, Jem finds his courage and takes action:
Jem threw open the gate and sped to the side of the house, slapped it with his palm and ran back past us, not waiting to see if his foray was successful. Dill and I [Scout] followed on his heels. Safely on our porch, panting and out of breath, we looked back.
This humorous episode from the novel is one of many that take us into the children's private world where they live according to their own rules until adults intervene from time to time.