What it is: Areas on the wood floor where softer parts of the wood appear to have been sanded more than other areas. Occurs between areas of annual rings or between mixed species of varying hardness together on a floor, such as in feature strips, borders and medallions.

Cause:
Using the wrong angles while sanding.

Cure:
Resand the floor using a slight angle with the big machine. A hard plate or multi-disc sander may be needed on softer woods.