How did the grass pattern develop?

From the Han Dynasty to the Southern and Northern Dynasties, the pattern of rolling grass was always used, but as shown in the sculpture of Yungang Grottoes, some new foreign technologies were added to the composition, such as adding animals to the pattern of rolling grass or juxtaposing two groups of rolling grass, which was introduced from Persia. On this basis, it developed into a popular curly grass in Tang Dynasty.