You see, the script reads the picture on a grid like this:
The first line of the script is:
[:DOMEFOSSIL,20, 0,3, 5,4,[1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,1,1,1,0]],
Where:
:DOMEFOSSIL is the internal name of the item
20 is the probability of finding that item. (If you look at RootFossil, it...