Block the defender's line of sight
Drop a piece between the defender and what it's guarding. Defender's still there, but its defence no longer reaches.
Bishop drops between queen and rook. Defender's line is blocked.
Bishop out. Diagonal open, mischief possible.
3 more clean runs (at any point) to reach Recall.
White's queen on a4 defends the rook on d1 along the a4-d1 diagonal.
3 more clean runs (at any point) to reach Recall.