She only allowed Xia Zhe to use these poisons as he faced a lot of danger in Country M. She was worried about him being in Sky City alone, so she applied poison on the daggers she gave him. He only needed to nick his opponent and make a small cut and the poison would spread through the person's body.
The poison that Qiao Mei fed Xia He was named "Paralysis Powder". After one drank it, one would feel as if one had been fatally poisoned. Even the doctors would not be able to find a cure for it. However, this was all just an illusion. After drinking the antidote, one would be fine and there would be no harm done to one's health at all.
"Help! Call an ambulance! Someone has been poisoned! Help!" Qiao Mei shouted towards the door.
