Everything that lives, must one day die, right?

Well, maybe not everything.

Consider the hydra.

It’s named after a many-headed monster from Greek mythology.

Chop off one head and two grow in its place.

That myth isn’t too far from the real hydra’s death-defying abilities.

They’re cousins to jellyfish -- see the resemblance?

But hydra live in freshwater.

Its body is a hollow column with walls only two cells thick.

Its head is just a bunch of tentacles surrounding a mouth, no eyes or brain.

The whole thing is about as long as a grain of rice.

The hungry hydra stretches out its tentacles to snag swimming prey.

Microscopic harpoons hook the water flea injecting it with paralyzing neurotoxins.

Then, it’s down the hatch.

The hydra uses those nutrients to make more hydra.

Check out this bud.

It’s a clone sprouting right from the hydra’s side.

Hydra can reproduce sexually too, but most often, they just clone themselves.

A chip off the old block!

Hydra are constantly regenerating their own bodies too, replacing all of their cells every twenty days.

They can do that because roughly half of the cells in their bodies are stem cells which can develop into all the different types of specialized cells you need to build, or re-build a body.

Stem cells only make up a tiny percentage of our bodies.

And our stem cells degrade over time -- that’s why we age.

But a hydra can make near-perfect copies of its stem cells … basically forever.

It’s called non-senescence -- biological immortality.

Having all those stem cells allows hydra to recover from all kinds of... damage.

Alright, here we go.

No body?

Not to worry.

No head?

No problem.

As long as the chopped off chunk has some stem cells, it's ready to regrow.

In a couple days, the severed head has a new body.

And the foot?

It’s got a brand new head!

Soon, they’ll both be as good as new… except for maybe some lingering trust issues.

To test the limits of their ability to recover, researchers came up with an experiment.

This hydra is genetically engineered so that under ultraviolet light its exterior cells glow purple and interior ones glow green.

Scientists basically blend up a bunch of these hydra.

Leaving a heap of mixed-up cells.

Right away, the cells start re-organizing.

Those purple outer layer cells migrate out.

The cells from the inside squirm back into the center.

The hydra dumps cells from the interior to restore its hollow shape.

The stem cells start dividing - and differentiating - to rebuild the rest of the animal.

Soon a head starts to form, sometimes a few little heads compete to be the new top.

After a few tumultuous days what was once a mixed up pile of cells takes on a familiar shape.

Researchers hope to harness hydra’s ability to regenerate to someday slow human aging, or even regrow damaged organs.