Harper Lee creates tension through the reaction of the adults to the mad dog. Jem knows that something is wrong, and he tells Calpurnia. Scout just thinks that the dog is acting funny. But when Calpurnia sees the dog, she
".....grabbed us by the shoulders and ran us home. She shut the wood door behind us, went to the telephone and shouted,'Gimme Mr. Finch's office!" (pg 93)
Then Calpurnia tells Eula May, the telephone operator, to...
".....call Miss Rachel and Miss Stephanie Crawford and whoever's got a phone on this street and tell 'em a mad dog's comin'? Please ma'am!" (pg 93)
Calpurnia decides to tell the Radley's. Jem and Scout followed her out the door. She yelled at them.
"You stay in that house!" she yelled (pg 93)
She goes to the Radley's and pounds on the door and yells to stay inside because of a mad dog. No one responds. Jem and Scout notice that everyone is staying inside and has locked his/her door. Then Atticus arrives with the sheriff, Mr. Tate. They watch the dog from a distance. Scout says,
"I thought mad dogs foamed at the mouth, galloped, leaped and lunged at throats, and I thought they did it in August. Had Tim Johnson (the dog) behaved thus, I would have been less frightened. (pg 94)
As they watched the dog approach, Atticus tells Calpurnia to go inside the house.
"Calpurnia opened the screen door, latched it behind her, then unlatched it and held onto the hook. She tried to block Jem and me with her body, but we looked out from beneath her arms." (pg 95)
The sheriff asks Atticus to shoot the animal because he was a better shot than the sheriff. Calpurnia prays,
"Sweet Jesus help him" (pg 96)
After Atticus shoots the dog, Jem and Scout try to join him in the street. He tells them to stay where they are. When he gets into the car with the sheriff, he tells Jem,
"Don't you go near that dog, you understand? Don't go near him, he's just as dangerous dead as alive." (pg 97)
The adults' reactions to the mad dog create the tension. It is obvious that the dog is deadly and could attack at any moment. It is also deadly after it is dead. They are going to send its head away to see what caused it to go mad.