What many pencils can do that magic markers can't

ERASE

Think of what you might need to do after making a mistake on paper.

This clue plays on the difference between pencils and magic markers—pencils use graphite, which can be erased, while markers leave permanent ink. The word "many" hints that not all pencils erase (like mechanical ones with non-erasable lead), but most do. It’s a straightforward comparison where the answer relies on a basic, everyday function of pencils.