system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why is it that things like ribbons curl up when dragged up against a sharp object like a scissors?
gpt
Imagine folding a piece of piece of paper in half, then opening it up.  The crease down the middle remains, and the paper no longer lies flat.  Imagine creasing the paper once every inch across, now it will curl up a bit.  When you drag a ribbon across a pair of scissors, you are creating one continuous crease.  This makes it curl up!