system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does a pencil eraser work? 

In addition, why do some work well, while others just smear around the pencil and leave a pink residue?
gpt
Erasers are made of rubber that, when dragged, will pick up the graphite flakes that are left on the paper from a pencil.  They literally abrade off the pencil marks.  Some erasers work better because they are softer and thus will conform more to the surface they are being applied to, while harder erasers will keep their shapes and not hit as much of the paper's surface area.