During the An Lushan (安禄山 ān Lùshān) rebellion in 756 AD the Tang general Zhang Xun (张巡 Zhāng Xún) was under siege by the forces of general Linghu Chao. Outnumbered twenty to one, the defending Tang forces soon ran out of arrows. To remedy this general Zhang ordered his men to make straw dummies (稻草人 dàocǎorén) and to dress them in black uniforms. That night the dummies were lowered over the city walls by ropes, accompanied to the beat of war drums (战鼓 zhàngǔ). General Linghu thought the enemy was launching a surprise night offensive and ordered his archers to shower the figures descending the walls with arrows. once the dummies wher riddled with arrows the Tang soldiers pulled them back up the walls and thus restored their supply of arrows. The next night the Tang again lowered the dummies but General Linghu ordered his men to ignore (不予理会 bù yǔ lǐhuì) them believing it was the same trick to get more arrows. When general Zhang saw that no one was firing at the straw dummies, he ordered that five hundred of his best troops (部队 bùduì) be lowered instead. They made a lightning raid (突袭 tūxí) on the encamped soldiers who were caught completely by surprise. The siege was lifted and general Linghu's army fled the field.
One method of using this stratagem is to create an illusion of something's existence, while it does not exist. Another method is to create an illusion that something does not exist, while it does.