On these rotting tree trunks, something is alive.

They can stand upright and produce spores.

But they're not fungi or plants.

When they're hungry, they spread across the forest, chasing food.

But they're not animals.

They're slime molds.

A slime mold exists at the boundary between liquid and solid.

Each one is like one big cell.

And it moves in a very strange way.

See how it pulses?

A little bit forward, a little bit back, spreading and searching for bacteria or fungi to eat.

But hold on!

Today we have someone else who moves in strange ways: the host of "It's Okay To Be Smart," Joe Hanson.

AMY: Oh hello Joe.

JOE HANSON: Hey there!

So from down here, it's pretty obvious that slime molds don't have legs or any appendages.

They move just by changing their shape.

AMY: Scientists want to know how this works.

So they brought a type of slime mold into the lab and fed it some oats.

At the University of California in San Diego, they put a piece of slime mold under a microscope, watched its weird, pulsating movement up close.

JOE: That motion is triggered by chemicals moving around inside it.

AMY: Water, moving in waves, carries tiny calcium molecules from back to front and back again.

The molecules are too small to see.

They're not those circles -- those are the slime molds' many nuclei, among other stuff.

But scientists can track the calcium flow.

In this video, it appears in light blue.

The calcium triggers a reaction that makes the cell wall contract.

JOE: The slime mold squeezes itself, almost like a water balloon.

AMY: That contracting-and-sloshing helps the slime mold inch forward, bit by bit.

And it kinda begs the question, could we build something that moves that way?

I mean, usually, we think of robots as solid, hard-edged machines that roll or walk from one place to another.

But what if they were fluid and powered by chemical reactions?

Like this Japanese "walking gel."

Maybe this is a really early step toward some hypothetical robotic goo that could squeeze into the narrowest parts of your body.

Hey Joe, imagine one of these inching through your arteries, helping clean them out as it goes.

JOE: Uuuh.

That might be kind of... creepy.

JOE: Hey Amy, I think I have a slime mold story even weirder than yours.

AMY: Oh yeah?

Try me.

JOE: Well, over on my channel we're going to look at some slime molds that actually help each other.

They're even kind of smart.

AMY: What?

That's nuts.

I'll be right over.

JOE: Thanks for having me on Deep Look, Amy.

And everybody, you should definitely subscribe.