Oh, I see.

And I have to agree with what you've said.

Without those lines, I would've believed that some magical process took place inside that metal strip,

but thanks to those lines, I can now speculate as to how this machine might've worked.

Maybe some kind of rolls were flattening the volunteer before the needle sewed her together,

or maybe the needle in itself was actually some kind of piston-needle, squishing a small area paper-thin, before the needle then just connects both sides, making it thus remain paper-thin.

It certainly is fun speculating on how a tf-process might work, so I'm always appreciating those hinting details.