I see two possible readings:Originally Posted by jiang
I had been sitting on the rock for so long that my body was becoming a part of it; my body felt as if it were part of the rock.
(1) It was uncomfortable, and I wanted to get up and go, but I didn't want to make any slight movements (in case the bear noticed my presence, and attacked me).
(2) It was comfortable, so comfortable, in fact, that I didn't want to move, not even an inch.
"to stir", to cause X to move slightly