Traditionally, a "worry stone" is a small polished stone held between the thumb and index finger, and rubbed with the thumb in an attempt to alleviate stress.

Over the course of several weeks, I have rubbed these erasers into various states of nothingness.  The smallest one has been around the longest, then the longer rounded one, then the squared-off longer one.  The one that looks new is pretty much un-rubbed, but is included in the set.

The two middle erasers have been rubbed between my thumb and index finger until a hole wore through the center.  They have a very pleasing feel to them, as they have been formed by hand, and without the use of tools.

This is the physical representation of countless hours of rubbing, and minuscule amounts of stress relief.