This is Hidden Brain. I'm Shankar Vedantam.

When they were teenagers, Ryan Brown and four of his friends

decided to visit a really old graveyard.

It was midnight, and they all piled onto an ATV

belonging to his friend David.

And this ATV is really just made for one person, so it's a vehicle with one big wheel in the front, two big wheels in the back,

and David was driving.

The rest of us were all kind of piled onto the back sitting on top of the wheel guards.

They took off down a dark country road.

There are no street lights.

He's going about as fast as he possibly can,

and nobody's wearing a helmet,

so if we crash, we're all dead.

Fearing for his life, Ryan spoke up.

And I said to David, over the road noise, the engine noise,

it would really be nice if you'd slow down a bit.

And he decided that was actually a great opportunity to turn off the headlights.

So we're on this dark country road, no lighting, no seatbels, no helmets.

Ryan panicked.

I kind of freak out.

I'm thinking, he's going to kill us on the way to a graveyard, no less.

So I start yelling at him and telling him he needs to slow down.

...