Building up a big mouthful of saliva seems to be a trick that pornstars and providers tend to use to make deep-throating more possible/enjoyable. It probably prevents cooties a little bit, too.

I first saw the saliva-covered dick in a porn movie about ten years ago, but i haven't experienced it from a girlfriend. If I need spit when I'm licking a pussy, I'm probably not doing something right; if I'm going for the backdoor, no matter what I add some industrial strength lube.

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seriousfun