Munch has a nightly (2am) play session with his stuffed Alex the bear.  
He grabs it by the back of the neck and talks to it incessantly for
fifteen or twenty minutes at a time.  He "kneeds" it, yowls and softly
murmurs to it, stands on top of it, and carries it around the house.
You should see him carry it.  He picks it up by the scruff of the neck,
(the bear is as big as he is), and carries it down the hallway.  If I'm
sitting in the living room, from my perspective, it looks like the bear
is magically walking down the hall, because Munch is not visible from
behind the bear.  He carries it in such a way that the bear actually
"steps" right down the hall.  It's priceless!

I once read that all of the varied vocalizations during play is the cat
using his or her imagination.