If something (a cock for example) hits the back of your throat in a certain way, the saliva just goes pouring forth.
There is some word for this activity, and I cannot think of it now, and it's when some guy is getting oral sex and he aims for that place in a woman's throat. Then, what happens is there is so much saliva that it's this huge mess but it can be also a turn on for the people involved.
I've had a few experiences where I've practiced this and well, it's rather intense. It's also a quick way to get your mouth wet if it's feeling a bit dry, too.
Too much information, I know!