When a demon resides within the body, it does not reside in a particular part of the body, but instead in the "negative" space. Meaning it can influence the body or body parts without relocating its position within the body. During a whole body possesion, the demon surrounds the entire body and takes control sending the person into a trance state.
Amorth, G., Stimamiglio, S., & Fasi, C. J. (2016). An exorcist explains the demonic: The antics of satan and his army of fallen angels. Sophia Institute Press.