If I were you, I'd wash all that salt off and put that rattler in the freezer. Then I would go and order a snake tanning kit from either WASCO or Rittel. Follow the instructions. Depending on how big those spots are the skin should be ok. Now if your "visitors" ate the skin and actually chewed holes into it, then it'll be ok for a wall hanging, but most likely not for a mount. But that again depends on the size of the holes. Small holes can easily be fixed with a good finishing apoxie and paint after the skin has dried on the form.
