I love nearly everything about this piece except the snarl :c Because you can interpret the Vogar as either Reptile or Mammal you have a big variation of snarls. This is very common, and if it is part of your art style, don't let me hold you back.
But just in case...
Canine Snarls
These are extremely easy once you get the hang of them, just a load of wrinkly flaps D:
http://yellow-eyes.deviantart.com/art/Don-t-146882343
http://yellow-eyes.deviantart.com/art/Fight-102635553
Feline Snarls
These are harder, for me anyways.
http://tarzman.deviantart.com/art/The-Lion-40561796
http://synnabar.deviantart.com/art/Were-Leopard-37639740
Snake Snarls
Again, pretty easy c:
http://gambitpk.deviantart.com/art/Untamed-Snake-139896168
In general, snarls and growls are pretty complicated, but will add great depth into your picture :D