Mario’s birth and defects (pp. 316–317)
An object of some weird attracto-repulsive gestalt for Charles Tavis, Mario treats C.T. with the quiet deference he can feel his possible half-uncle wanting, and stays out of his way as much as possible, for Tavis’s sake.
Context
Here the book finally says the quiet part: "possible half-uncle." The question the hidden pregnancy and the StairMaster timeline and the shared comb-over have been circling gets named, once, in passing, and then folded into a note about Mario's tact. And the tact is the real content — Mario, alone in the family, senses the "attracto-repulsive" thing C.T. feels toward him and manages it kindly, giving the man the deference he can tell he wants and otherwise staying out of his way "for Tavis's sake." The one Incandenza who might most embody the family's central unspeakable is also the one who handles it with the most grace, absorbing the uncle's discomfort so the uncle doesn't have to.