If Only Mortality Quotes

How we cite our quotes: (Chapter.Paragraph)

Quote #10

After using every hand signal for death we know—finger across the throat, finger gun to the chest, sword to the stomach—and repeating the word "cancer" over and over, they seem to get it. (53.19)

The Ishibashis don't get it, though, and Aiko calls the next day to say her parents are worried about Sophie. Why did the Ishibashis ask Corinna and her dad about Sophie, watch them mime several kinds of violent death, and then invite them to their home?