Scott has flunked his math test, and he blames his teacher, Mrs. Whitman, for this. He also blames her for missing out on a trip to Yellowstone that would've been his reward for passing the examination.
Out of revenge, he's kidnapped her dog Gloria and is holding her for ransom. Scott has phoned up Mrs. Whitman to tell her that he has the dog. At first, Mrs. Whitman seems to think it's just a nasty prank and that her dog will soon be returned to her.
But she's soon proved wrong when Scott demands a sum of money for the dog's safe return. After Scott makes his demand, there's a pause on the line before Mrs. Whitman asks the dognaper how much money he wants. When Scott says that he wants $1,000 in one-hundred-dollar bills, Mrs. Whitman is somewhat taken aback: "A thousand dollars?"
Note the use of italics. It tells us that Mrs. Whitman is emphasizing the amount that Scott demands, as if she can't quite believe that someone would kidnap a dog for such a large sum of money.
Mrs. Whitman can only protest that she doesn't have that kind of money. What's more, she doesn't know where she can get it. Scott recognizes the same kind of whiny tone in Mrs. Whitman's voice that he uses on his mother when he tells him off for failing to take responsibility for his actions.
This information gives us an insight into what kind of young man Scott is; he's someone who never blames himself for what he does. And it's the same here. As far as he's concerned, it's Mrs. Whitman who's to blame for her dog's kidnapping, not him.