Just dreaming, almost certainly. Obi gets such active dreams that not only do all of his paws twitch (the twitching can be very jerky, too), but so do his ears and his tail . . . and he'll chatter in his sleep. I wish I knew what he was dreaming about! I try not to move and wake him, because it's so funny, but I usually start laughing and that wakes him up. I wonder, even if he could somehow tell me, does he even remember what he dreamed about (I remember my dreams, but my husband doesn't remember his)?