Elder Sun used the Yin Yan Hawk Plant to feed the Three Serpents Fire Cauldron's Medicinal Treasure for many years. In an attempt to upgrade his Scarlet Refined Serpent Physique to the Scarlet Dragon Physique he had started to use the Fire Dragon Plant instead of the Yin Yan Hawk Plant. Although theoretically it was supposed to work, it actually didn't, for some reason. Moreover it even caused hindrances for his cultivation. Elder Sun was puzzled by this development and couldn't find a reason of it.
Eventually, Elder Sun came to Li Qiye and asked for help. Li Qiye examined him and the Three Serpents Fire Cauldron and then explained that Elder Sun used the wrong plant and gave him pointers on how to change the situation.
It is as small as a fist and had three serpents intersect at the mouth of the cauldron.