What do the group of kids think they see as they are walking away from Radley place?

Dill develops an insatiable curiosity about Boo, and wants to lay eyes on this strange "phantom," who is said to walk about at night looking in windows. Dill dares Jem to go inside the boundary of the Radleys' front gate. After three days of hedging, Jem's fear of Boo succumbs to his sense of honor when Dill revises his terms, daring Jem to only touch the house. Jem finally agrees to do this. He runs, touches the house, and the three scramble back to the Finches' porch, where looking down the street to the Radley house "we thought we saw an inside of a shutter move. Flick - and the house was still."