Their mate or yours
解杀还杀 — parry by mating first. Black's chariot on f1 threatens ...Rf0 mate: the g2 knight has sealed e1, and the moment the king leaves e0, d0 falls under the checking chariot's rank. No passive answer exists — a chariot one step away cannot be blocked, and every flight square is already spoken for. When defence is hopeless, the only pass is attack: Red's own mating net needs exactly one move, and Red moves first.