Kill Box Mate
A Kill Box Mate uses a queen and rook to confine the king in a small area. One heavy piece gives mate while the other supports it and controls nearby escape squares.
What to look for
Look for a compact queen-rook net: an adjacent rook, a rook two squares away on a rail, or an adjacent queen with the rook supplying the fence.
Recognize the mechanism
Separate the three training families: Adjacent Rook has a rook mating beside the king under queen protection; Rook Rail uses the distinct two-square rook relationship supported by the queen; Queen Fence has an adjacent mating queen and a rook that materially supplies confinement.
Common practical mistake
A rook or queen merely being present is not proof of cooperation. Identify which piece checks, which supports it, and which local escape squares are removed. Choose the subtype by that mechanism.
Training goal
Train your eye to build a mating net instead of only looking for one-move checks.