from Sindy Tsure:

Just a little script to tell you about the first thing it collides with. Useful for figuring out what a ghost prim is. Had to dig around for this last night so I figure I'll post it here - easier to find next time.

Put the script in a cube, move the cube a few meters over the suspected ghost, touch the cube.

default
{
     state_entry()
     {
          llSetStatus(STATUS_PHYSICS, FALSE);
     }

     touch_start(integer total_number)
     {
          llSetStatus(STATUS_PHYSICS, TRUE);
     }

     land_collision(vector position)
     {
          llOwnerSay ("hit land! no objects here..");
          llResetScript();
     }
     
     collision_start(integer count)
     {

          // todo: notice llDO returing a key and spit out web link to profile instead
          llOwnerSay ("hit '" + llDetectedName(0) + "' owned by " +
               llKey2Name((llDetectedOwner(0))));
          llResetScript();
     }
}