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Guaranteed Human.

If you sit on the banks of the estuaries in Southern California and Baja California,

the seat of your pants will get super muddy.

But also, you'll likely see schools of silvery fish swimming through the water.

If you watch closely, some of those silvery fish will begin behaving rather strangely.

They'll shoot upwards quickly, breaking the water surface and creating these super conspicuous ripples on the surface.

Or they'll turn on their sides as they scratch their bodies against a rock.

As they do this, their silvery bellies reflect the sun and create this quick and vibrant flash of light.

Why are they doing this?

These fish are bite-sized to the sharks and the predatory birds that sometimes roam these estuaries in search of food.

Shouldn't they be trying to look a little less conspicuous?

Why are they drawing so much attention to themselves?

Well, it's me speaking, so you've probably guessed that the answer is parasites.

Today, we're going to talk about U-Hoplorcas Californiancis, a brain-infecting parasite of

California killifish, which are the silvery fish dancing through the waters in California

that we were just talking about.

Welcome to Daniel and Kelly's extraordinarily infected universe.

Hi, I'm Daniel. I'm a particle physicist, and I hope I'm parasite free. Hello, I'm Daniel. I'm a particle physicist and I hope I'm parasite free.

Hello, I'm Kelly Weiner-Smith. I study exactly what we're talking about today.

And I'm okay if I'm harboring a parasite or two, depending on what they are.

All right, well, that was actually my question for you, Kelly.

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