Ancient Chinese tended to bury treasures with them. Not surprisingly, tomb robbery was once rampant throughout the country. To prevent outside invasions, Emperor Qin Shihuang ordered a full range of precautions. It is said that besides poisonous mercury, booby traps with automatically ejected arrows were installed in the tomb chamber to deter would-be robbers. Anyone who dared to break in would certainly die a violent death.

However, all those alleged lethal weapons have been buried under earth for thousands of years. Would they still function adequately now? Most people believe that the crossbows would still shoot arrows if they are triggered. Guo also agreed so after he carefully studied ancient smelting technology recorded in historical books.

In a modern test, a coating of chromate was found on the surface of weapons excavated along with the terracotta warriors. This coating served to make bronze weapons rust-resistant. Thus, it is highly likely that the automatic crossbows may function well even after thousands of years.

Guo speculated that these crossbows were the first automatic burglar-proof devices in the world. "Craftsmen were ordered to fix up these crossbows in such a way so that any thief breaking in would be shot." He quoted a line in Records of the Historian to support his prediction.