its possible the nuns story was a variation of this, theres quite a bit of folklore attatched to bells and mentions of animal sacrifice.
http://www.mybeijingchina.com/beijing-attractions/drum_tower_bell_tower.htm
According to legend, an official named Deng tried unsuccessfully for over a year to cast the bell. On the eve of the final casting, his daughter, fearing that further delays and loss of working time would bring blame on her father, decided to sacrifice her life in order to move the gods to bring about a perfect casting, and threw herself into the molten bronze. Her panic-stricken father could only recover a single embroidered slipper from the flames. The casting was a success and the emperor, moved by the young girl's spirit of sacrifice, named her the "Goddess of the Golden Furnace" and built a temple in her honor near the foundry. By the ordinary people she was remembered as the "Goddess Who Cast the Bell."
After the bell was installed, the chimes could be heard clearly and resonantly all across the city. But on stormy evenings, the bell would emit a desolate moaning sound similar to the word xie, which means "shoe" in Chinese. Recalling the old legend, mothers would comfort their children with: "Go to sleep! The Bell Tower is tolling. The Goddess Who Cast the Bell wants her embroidered slipper back."