The "black bird' and "white snake"

I've been wondering what the black bird and white snake symbolize, especially the scale given to Ritchie.  I can see them being symbols for death, satan, racism, but what about their interactions with Ritchie?  What does the transformation from snake to scaly bird mean?  Again, what is the significance of the black scale?  Is it a kind of reminder, or is it a mark?