Morning sunlight slanted into the courtyard as Chen Xuan crouched beside the mechanism crossbow, tightening the last vine cord. The contraption, pieced together from bamboo poles and a crooked bow, sat lopsidedly atop a stone platform. Its firing groove tilted slightly upward, like a beast poised to pounce.
Mo Feng stood several paces away, clutching the freshly drawn defense map in his hand, his brows knotted tight. "Can that thing really work?" he asked Chen Wuya in a low voice. "We don't have spare iron nails to waste."
Chen Wuya did not answer. He merely nodded at his son.
Chen Xuan drew a deep breath and slipped an iron nail into the groove. He pulled the trigger cord, then gave it a hard yank. The bamboo arm snapped back violently, sending the nail tearing through the air in a wildly irregular arc. It somehow curved around the pile of firewood blocking its path and drove straight into the heartwood of a pine tree thirty zhang away, its tail end buzzing with vibration.
Mo Feng froze, then rushed over and yanked out the nail. He examined the direction of its mark, then turned back to stare at the mechanism crossbow's structure. His expression changed.
"The angle was off by three inches, but the force didn't disperse," he murmured. "Instead, the twisting momentum drove it deeper through the wood."
Chen Wuya crouched down, his fingers brushing over the bow arm bound tight in the reverse direction. "He's right."
"What?"
"Sometimes, pulling force backward hits harder than charging forward." Chen Wuya looked up. "That was the first thing I taught him."
Mo Feng knelt on one knee and carefully inspected the stress points at the joints. The place where the bamboo arm met the frame had been wrapped in three layers of vine