one of several parts or pieces that fit with others to constitute a whole object
Similar to the cutting away of infected tissue in order to allow the surrounding area to heal, Dad has to cut away the destroyed sections of the chest in order to rebuild it. Although it is used as a noun here, "section" can also be a verb (the Latin "secare" means "to cut" and can also be seen in "dissect").
He also has to cut out some sections that he destroyed when he kicked the chest on The Day Our Life Fell Apart.
make complaining remarks or noises under one's breath
Compare with "murmur" in this list--they are both onomatopoeic words that sound like what they describe (which in this case are sounds too low to be accurately described). But "mutter" is used as a verb here to connect to one person, while "murmur" is used as a noun to connect to a noisy crowd.
Dad mutters a lot of things but I can’t hear them and I don’t care because at least he’s not yelling.
In school, recess usually involves outdoor play. This should be a time that most children would look forward to, but because Caitlin struggles with autism, she would rather find a recess ("an enclosure that is set back or indented") where she would be out of reach of the screaming bunch of runners, grabbers, and pushers.
Recess I hate because everyone screams and runs around crazy and grabs you and pushes you and you have absolutely no idea what will happen next.
characteristic of false pride; having an exaggerated sense of self-importance
The definition does not apply to the example sentence, since the adjective is describing the character's face (the swollen face would actually decrease a person's sense of self-importance). Here, "swollen" is the part participle of the verb "swell" in its meaning of "expand abnormally."
His face is swollen and his voice cracks even though he only has one word to say.