Silence
A frequency you can be trained to read.
The author was taught, by his mother, that silence has a shape — that a room can tell you exactly what is missing if you know how to listen to the quality of what is not said.
Much of the book's tension comes from this literacy: sentences that record what was withheld as carefully as what was spoken.
From the text
“The silence that has a specific frequency, a specific quality, that tells you exactly what shape of thing is missing.”
Prologue