Pretty sure this is either a joke headline or a misrepresented one. I did learn that the world's thinnest endoscope is the width of a human hair, though
I mean, the first thing I think of is graphine. It's a sheet of carbon that is literally one atom thick. Naturally, it's a manmade substance. Even ignoring that, there are butterflies with "hairs" that are so small that they can separate waves of light to give the illusion of it being blue.
I did get the joke, but it wasn't exactly a good one. It reminds me of an example I've recently heard.
You can ask why parachuters wear a helmet. What's it gonna do if they do crash into the ground? It is funny because they do wear helmets. If you asked why parachuters wore ballet shoes, then it wouldn't work because they don't wear the shoes. For the same reasons, I see this joke as still working, but it doesn't exactly strike a chord due to it not being an extremity.
Admittedly there are situations where the helmet probably is helpful, but, to quote Jerry Seinfeld:
"If you jump out of that plane, and that 'chute doesn't open, the helmet is now wearing YOU for protection."
You can ask why parachuters wear a helmet. What's it gonna do if they do crash into the ground? It is funny because they do wear helmets. If you asked why parachuters wore ballet shoes, then it wouldn't work because they don't wear the shoes. For the same reasons, I see this joke as still working, but it doesn't exactly strike a chord due to it not being an extremity.
"If you jump out of that plane, and that 'chute doesn't open, the helmet is now wearing YOU for protection."