To scratch lightly to find s.t. (as a cat or dog); (for a person) to rummage through a pile of s.t. (using both hands in a scratching the surface type of movement); to scrape things (focus) lightly to one side [-an](as when looking for s.t.).
The -an imp. is used when moving s.t. out of the way. The -un imp. focuses on what one is looking for or what one is rummaging through.
Scrape that trash to the side. Maybe you can find your ring there.
Rummage through that trash to find your marble.
Who was rummaging through this trash?