Interesting thread. It brought back memories!
Actually, this was one of the first things our family noticed about our little guy. When he was maybe 2, he always had a small action figure in his hand, and he would twirl it over and over in his hands while focusing on it and moving his lips without words coming out. My older kids thought it was a little freaky, but it kept him happy and quiet in the car, in church and wherever we were. He slept with the action figure gripped in his hand, and if he couldn't find whichever was his favorite at the moment was really the only time he'd have melt-down. He's 10 now and still does it from time to time.
I asked him why he would spin it around and what was going on in his head, and he told me that he could picture stories as they happened when he was spinning it.