Tom's preoccupation with the murder is replaced by worry about Becky's absence from school. When he learns she's ill, he fears she'll die.
Tom's sense of self-importance as a romantic hero overwhelms his ability to realistically see his crush's illness. In essence, he pities himself more than her.
Tom remains despondent, so she gives him an awful-tasting painkiller. Tom avoids it by requesting it so frequently that she gives him the bottle to self-administer his doses.
Tom's disobedience saves him from the unnecessary medicine that his Aunt unreasonably forces on him. He once again reverses the power balance, showing how he understand the rules of human behavior and inconsistencies of adults better than she does in comprehending that, like a child, she won't want to do what's expected of her.
Tom gives some of the medicine to the cat, which goes berserk. When Aunt Polly asks Tom what happened, he lies, then confesses. She hits him but then Tom explains how awful the medicine tastes. She then says that Tom doesn't have to take it.
Though he only meant to have fun, Tom's mischief harms the cat. However, it also shows Aunt Polly that she was more worried more about the cat's health than Tom's.
Tom arrives early to school. When Becky arrives, he plays at "doing all the heroic things he can conceive of" to get her attention. She tells him to stop "showing off". He's heartbroken.
Tom's romantic play-acting no longer interests Becky. She has outgrown it. Tom, however, continues to follow his romantic ideal even after her rejection, now acting dramatically heartbroken.