In To Kill Mockingbird, how is tension created when Jem and Scout get attacked by Bob?

It is in Chapter 28, which concerns before, during and
after the pageant, that narrates the attack on Jem and Scout. Note how this represents a
new moral "low" for Bob Ewell, as, to cowardly to attack Atticus directly, he decides to
move against him indirectly by attacking those who are most vulnerable and unable to
defend themselves - his children.

Lee is very skilful in
how she creates suspense in this chapter - note how it is given a false climax with
Cecil Jacobs jumping out on Jem and Scout in the pitch black. This has the effect of
lulling us into a false sense of security, much as in horror movies there is a false
climax before the "real" horror begins.

It is when Jem and
Scout are returning to their house after the pageant that Bob Ewell strikes. Note how
tension is created immediately by the fact that Jem and Scout are alone and isolated in
the dark. When Jem thinks he hears something and stops Scout and makes her listen, note
how Scout describes the silence:

readability="5">

This was the stillness before a
thunderstorm.

This sentence
clearly indicates that the "storm" is just about to break and danger is going to come
upon the children.

Tension is also raised by the sound of
their pursuer, who Scout names "Shuffle-foot." The sound he makes allows them to tell
when he stops merely following them and begins to run after
them:

readability="10">

Shuffle-foot had not stopped with us this time.
His trousers swished softly and steadily. Then they stopped. He was running, running
toward us with no child's steps.

"Run, Scout! Run! Run!"
Jem screamed.

The
onomatopoeia in the swishing of the trousers and then the realisation that their pursuer
is not a child, but an adult, combined with the screaming of Jem serves to greatly
heighten the tension as we wonder what will happen.