Sanzang is singing Heart Sutra ( https://en.wikipedia.org/wiki/Heart_Sutra ) , his favorite Sutra . Maybe he gives some actions as a bonus so the demons can understand the Sutra more better , lol .
The Tang dynasty's king probably kicked Sanzang out of the country to retrieve the scriptures because he destroyed everything whenever he sang this sutra , lol .
We only asked him to recite mantras, right.......Hey, you guys really just told him to recite Buddhist mantras right?discovered that
all of the five Skandhas are equally empty,
and with this realisation
he overcame all Ill-being
“Listen Sariputra,Suddenly,While practicing deeply with
the Insight that Brings Us to the Other Shore,
An excerpt from the Heart Sutra, based on the translation by Thích Nhất Hạnh