The Meaning of Anatta - Is it rupa that walks?

Questioner: In the section of “Clear Comprehension” (sampajanna) in the “Satipatthana sutta,” it is explained that when we are standing, we should know that we are standing, when walking, sitting, bending or stretching, we should know that we are doing this. We should know the characteristics of the different postures. When we know that we are walking while we are walking, is that the practice with regard to the rupa that walks?
Sujin: If there would be no rupa, could we walk?
Questioner: If there would be no rupa, it would be impossible to walk.
Sujin: When you are walking there is one characteristic of rupa appearing at a time and it can be known as it appears through one doorway.
Questioner: Is it rupa that walks?
Sujin: The rupa which appears, no matter whether we are sitting, lying down, standing or walking, appears through the sense-doors or through the mind- door. It is anatta, it appears anyway because of the appropriate conditions; it is of no use trying to select a particular rupa.