One of my cats, a large male, likes to jump up on me in bed and rub against me while I pet him. This is fine, but I found it disconcerting that the cat would often drool as he did so, droplets of cat spit pattering down on my covers. -- What was going on? -- Was he preparing to eat me?! So I asked my vet about the behavior... Once he had established the context in which the drooling occurred and I reassured him that the saliva wasn't bloody, the vet felt that the drooling was a manifestation of arousal of the cat's pleasure center. This is an individual distinction, and not all cats do it. It was just an involuntary way that he showed his enjoyment of our interaction. So I keep a tissue handy, and wash my covers often...and I'm glad that the human species doesn't manifest pleasure in interaction by drooling!