Pretend Injured To Strike Surprised

The Strategy Of Injuring Yourself To Win The Enemy's Trust
Means that you will pretend you are injured by your enemy or another enemy. When your enemy really know and believe that, he will be relaxed. This is the time to attack by surprising your enemy and that leads to victory.
Pretending to be injured has two possible applications. In the first, the enemy is lulled into relaxing his guard since he no longer considers you to be an immediate threat. The second is a way of ingratiating yourself to your enemy by pretending the injury was caused by a mutual enemy.
People rarely inflict injuries on themselves, so when they get injured, it is usually genuine. Exploit this naivety and make the enemy believe one's words; then the trick to sow discord among enemies will pay off. In this case, one takes advantage of the enemy's weakness, and makes the enemy look as if he were a naive child easily taken in.
Edo Period Japan
During the Tokugawa period, Kaei Juzo a former spy had come under suspicion and was in danger of being assassinated.
It turned out that the man sent to kill him was a former acquaintance called Tonbe. Not wishing to kill his old friend, Tonbe and Juzo worked out the classic ploy as follows.
Tonbe brought Juzo back as a prisoner to the Shogun. Juzo begged the Shogun to allow him one last dignity, permission to commit Harakiri. The Shogun, curious to see the notorious spy's bravery in death, allowed him that privilege. Juzo was given a tanto (dagger) that he plunged into his belly, and, cutting sideways, spilled his intestines onto the ground before falling over. The guards removed the body and threw it in the castle's moat. A short time later Juzo quietly swum to shore and escaped the district.
Knowing that his warrior's reputation would merit him the right of committing Harakiri, Juzo had strapped a dead fox across his abdomen, when the fox's intestines spilled out it was indistinguishable from human intestines.
This stratagem is often used with Stratagem 33. Pretend to take no notice of being monitered and feed the enemy with information which he won't suspect is false.
During the Spring and Autumn period, King He Lu wanted to the prince of Wei Qing Ji. His advisor Wu Zixu told him that Qing Ji is a powerfully-built man and that to kill him, they must call upon Yao Li.
Yao Li deliberately insulted He Lu in front of others. He Lu ordered his right hand to be chopped off. Yao Li then went to seek refuge in Qing Ji's domain.
Suspicious, Qing Ji sent men to Wu to check out Yao Li. A few days later, the men returned and reported that the king of Wu beheaded Yao Li's family and had their bodies burned in public. Yao Li cried and vowed that he would make the king of Wu pay the blood debt.
Thereafter Yao Li became Qing Ji' confidant. One day, while they were on an expedition to attack Wu, Yao Li sprang on Qing Ji and killed him. After killing Qing Ji, Yao Li slit his own throat.
The king of Wu became the dominant power of the south.