Once upon a time, two herons had built their nests on the roof of a temple at Tientsin. For long years, dust had accumulated in the shrine within which lived a huge serpent. Whenever the young ones of the herons were ready to fly, the serpent would creep towards the nest and swallow everyone of them. This made the herons very sad.
It happened for three years and now people believed that the herons would no longer build their nests there. Nevertheless, the following year they came again. When it was almost time for their young ones to take wing, they flew away. The herons returned after three days and went straight to the nest to feed their young ones. At that very moment, the serpent crawled up to reach his prey. As soon as he neared the nest, the parent birds flew out and screamed loudly in mid-air.