While doing some research, I found out some of the Mongols' most deadly seige technology included cats, swallows and even human fat!
The first large-scale Mongol attack in Xi Xia happened at the mighty fortress at Volohai. Unable to breach the walls of Volohai, Genghis Khan resorted to a clever trick. He sent a message from his encampment to the Tangut general announcing that he would end his siege in exchange for a gift of one thousand cats and ten thousand swallows. Astonished by the unusual request, the fortress commander gratefully complied. After the animals arrived in the Mongol camp, Genghis Khan ordered his men to tie a small cotton-wool tuft to the tail of each creature then set the tuft afire. When the panicked and frightened animals were turned loose, they made directly for their nests and lairs inside Volohai, igniting hundreds of small fires. While the panicked defenders were preoccupied with putting out fires, Genghis Khan's warriors stormed the city in conquest.O.K. Now I might have held off against the cats. The 10,000 swallows with burning tufts of cotton on their tails setting everything on fire would have really started to bother me.The Mongol siege against the walled town of Kusong exemplified Koryo's [Korea's] heroic resistance. General Sartai brought the full array of his medieval assault weapons to bear against the city's defenses. While Mongol troops attempted to undermine the defensive walls by tunneling under them, formidable lines of catapults hurled large boulders and molten metal at the town. Special assault teams used siege towers and scaling ladders against the earthen walls and pushed flaming carts against the city's wooden gates. Perhaps the most grisly tactical weapon used at the siege of Kusong was the catapult-launched fire-bomb. The Mongols boiled down their captives and used liquified human fat to fuel a weapon which produced fires that were practically inextinguishable. Kusong's defenders refused to surrender and stubbornly held on for thirty terrifying days and nights. An old Mongol general, inspecting the ramparts during the siege, commented that, "...I have never seen [a city] undergo an attack like this which did not, in the end, submit." In the end Kusong remained in Koryo's hands.
But I tell you what: The burning fat of my melted friends being spewed all over my fort in viturally inextinguishable hell pretty much would have put me over the top.
"Mr. Mongol. Please stop throwing the burning fat of my men all over this fort. You can have it. It's drafty anyway."