If you’ve had a traumatic brain injury you already know what I’m writing about. If not, here’s some insight into how our brains work.

I’m collecting environmental samples today so I threw my gear into our antique Chevy Suburban, kept in barely useable condition to show the public how carefully we watch after their dollars. I fired it up and heard a faint, regular squeak that made me wonder if a sandpiper built a nest underneath and was sitting on a clutch of chicks.

I listened and was positive something was amiss. The truck was parked outside of a trailer office and I wondered if there was a swallow’s nest atop an air conditioner and if the swallows were angry at me for invading their presence.

Whatever it was, I had to check it out.

I left the truck running, got out, and the peeping stopped. Ah, I thought, sandpiper chicks, silent now at my step. But to be thorough – every good scientist is thorough – I checked the back, too, and eyed the air conditioners. Nothing up there, but I heard the chirp again, like it came from inside the truck.

Great. What morsel did someone toss in here? I lifted up the door and rummaged through Cubitainers and tubing and couldn’t find a thing. Very weird because something back here is still making noise. I heard it again and saw a faint black swish stream across my periphery. Shocked now – we talked about snakes in our safety message this morning – I stepped back to survey the inside of the truck again.

Then – then! – I saw it and heard it again. I almost wish it was a baby cottonmouth with a mouse in its fangs, crying and squealing. Instead, it was something mundane and boring, like most mysteries. I stepped back and waited until it happened again. It was the wiper blade, dry against a dry window, with the motor pushing it hard enough to chirp.

And that’s how it works. The brain fills in empty spaces with ideas that sound reasonable.