"it was Ash Wednesday by the calendar and the first folk he saw were Mexicans with sootmarks on their foreheads"
A cross of ashes on a worshipper's forehead on Ash Wednesday
Creative Commons Attribution Share AlikeA cross of ashes on a worshipper's forehead on Ash Wednesday - Credit: Edi Wibowo

Ash Wednesday marks the first day of Lent, occurring 40 days (not counting Sundays) before Easter. It is named after the practice of placing ashes on the foreheads of adherents as a sign of repentance.

Appropriately enough, on the day Billy buries his younger brother, ashes were also used in ancient times as a symbol of sorrow and mourning.