collabertive drawing

How does someone else working on your drawing add or take away from your drawing?

When I started my drawing I pictured two little penguins on there way to school it was snowing and they were almost there. When i got back to my drawing i saw a penguine covered in "snow" and the other had a lot of snow on his back. I didn't really like what i saw because it was not what i had in mind so I took off the snow and tried to paint the penguin back to its color