There is a mod that allows you to do that, it just requires a bit of work.. it isn't like the Tails mod or More Player Models. It allows you to implement 3D models, such as 3D tails and ears, like Aphmau does it (Aphmau uses a custom mod made by her crew, but this is the same idea), onto your Minecraft Character.
Mods: BlockBuster & Metamorph
It takes a bit of work but it looks good. You need Blender and some other things.
Link to a Youtube Video on how to do this:
iiRaeRae, The problem is that they still don't have animations. It isn't that we haven't figured out how to use BlockBuster and MetaMorph to make the object models, it's that we can't figure out how to make them animated in MineCraft.