I know the difference, professionally, between a person who cannot answer a question and a person who will not, and the difference shows up in the shape of the evasion.

A person who genuinely does not know gets flustered in a scattered way; their dodges point in different directions, because they are improvising.

A person who knows the answer and has decided to withhold it dodges with a strange consistency; the swerves all curve the same way, toward the same ditch, because they are all protecting the same hidden thing.

My mother the cake, my father the coupons, the ask-her and the ask-him were not the scattered fumbling of two people who had never tallied a budget.