What does Cecil Jacobs do before the pageant, which help set up the incidents which occur after the pageant?

While on their way to the pageant, Cecil Jacobs jumps out from behind a tree and scares Jem and Scout.  It is this incident which makes Jem and Scout think Cecil is up to his silly tricks again, when they hear noises on their walk home.  Unfortunately, however, it is not Cecil, but rather Bob Ewell, who is looking to harm Jem and Scout.  After a rumble with Mr. Ewell, Scout manages to break free, but Jem is left behind.  Later Sout learns that Jem was brought home safely by Boo Radley.  It is at this point that Jem and Scout realize Boo's true heart.