In the following poem, which sentence describes the scene and "courier" at that time?

Riding a princess and laughing in the world of mortals, no one knew it was litchi.

"The world of mortals rides a princess and laughs. No one knows it's litchi." It is said that Yang Guifei likes to eat litchi, and the emperor rides a fast horse, which means that he is very fast, but he can only see the thick smoke but not the fierce horse that flies by.