We all know how the journey through the digestive system ends.

[beep] But few give much thought to how it begins.

If the mouth is the doorway [ding dong] saliva is the greeter.

One of the most important substances produced by the body, yet one of the most overlooked, and to many, one of the grossest, conjuring of words like [bleep] What?

What did I?

What did I say?

[bleep] I can't?

M-O-I-S-T.

I can't say?

[bleep] All right, fine then.

Let's move on.

Moist.

[music playing] Perhaps the best way to really appreciate saliva is to learn what it would be like to live without it.

I give you the time honored scientific tradition of the salt challenge.

[cheers] Six crackers, no water, one minute on the clock.

[ticking] [ding] [ding] [ding] [ding] [ding] [ding] [buzz] (MUMBLING) I can't swallow.

There's, there's nothing in my mouth.

To make saliva cells pump out salts.

And because of osmosis that draws out water.

Unlike with tears or sweat, that salt is then taken back up by the glands, leaving you with something that's about 99% water.

The other 1% is proteins and other molecules, which gives saliva that sticky feel you know and, well, have feelings about.

That 1% is also where most of the cool spit happens.

But not all saliva is secreted equal.

We pump out two different brands of mouth juice.

Unstimulated saliva is secreted by hundreds of tiny glands all over our mouth.

And we make it essentially all the time.

This saliva contains a special ingredient called mucin, which is a protein that loves to soak up water, creating a kind of gel that forms a thin protective coating all over your mouth parts.

Mucin is basically why saliva sounds like this.

[mouth noises] On the other gland, stimulated saliva is, well, what it sounds like.

It flows when we smell something delicious or chew.

It really doesn't matter what you chew.

It could be anything.

But I suggest food, or maybe gum.

We have special sensors beneath our teeth.

When they feel the pressure mastication they send a signal to crank up the spit factories.

Super sour or salty foods also stimulate saliva, basically to dilute the acids or salts and protect you mouth.

And you can test this.

Just put a drop of lemon juice on your tongue and wait for the floodgates to open.

[rushing water] Lots of people think sugar causes tooth decay.

But it's really caused by acids released by bacteria that eat the sugar.

Saliva dilutes that nasty stuff so you can keep your teeth.

And since we make less saliva when we're asleep, that's prime time for tooth decay.

But you always brush before bed, right?

[horn] You probably know there's two salivary glands under your tongue.

But most saliva that comes from chomping and tasting is made by the parotid gland, situated between your ear and mouth.

It's not here or here so much, but right here.

Now obviously, this type of saliva makes eating possible by lubricating your food.

But it also contains a bunch of proteins.

Now the exact saliva protein mix varies throughout the day.

But the most abundant is amylase.

Amylase is an enzyme.

It chops long, complex sugars, like starch, into simple ones.

Because glucose is what cells crave.

Try this.

Hold a bite of cracker in your mouth without swallowing, and let your saliva go to work.

After a few minutes a sweet taste begins to take over as the starch in the cracker is broken down into simple sugar.

Sweet.

Proteins are one of the reasons babies drool so much.

Baby saliva contains enzymes that help digest milk.

So when milk is your only food, you make a lot of drool.

In fact, enzymes from saliva that break down starch, protein, and fat are manufactured on large scales and added to laundry and dishwashing detergents to help them, literally, digest stains.

In most cultures spitting on someone is just about the grossest worst thing you can do.

Yet we don't mind swapping spit with the people we love.

At least that was true before you watched this video.

Now I don't expect that we'll all stop being a little weirded out by saliva any time soon.

But if you take a second to chew on the idea, when it comes to multipurpose liquids saliva even puts sriracha to shame.

You know what?

Drool rules.

Stay curious.