At the Dragon Well Tea Factory in Hangzhou.

Part of the tea manufacturing here is they "stir" the freshly dried tea leaves in an iron pot by hand using some sort of plant oil as a lubricant. They say they have to stir the leaves for several hours. They say this is to make the tea taste better.

What I think they are doing is this. By stirring the tea leaves they are causing micro fractures in the leaves. So when you pour hot water on them later, the water enters the fractures causing the leaves to stew more completely and therefore more tea flavor comes out.