The tongue is the only tool that sharpens with use.

The tongue is the only instrument that doesn't wear out with use.
The tongue like a sharp knife... Kills without drawing blood.
The tongue is the only tool that gets sharper with use.
The tongue is the only instrument that gets sharper with use.
Keep thy tongue from evil, and thy lips from speaking guile.
A sharp tongue is the only edge tool that grows keener with constant use.
Handle your tongue as your money, spare both till you're asked.
Kind words can be short and easy to speak, but their echoes are truly endless.