I am trying to do automatic weighting on this object, but I am getting a "Automatic Heat Weighting: Failed to find a solution for one or more bones".
I have tried multiple things to fix this:
I still cannot get it to work. Here is the file if you want to take a look:
Try adding a subsurface modifier to the meshes you want to parent before you parent them. You can remove it later. For some reason it should work.
By your question I suppose that you are using the "With Automatic Weights" method.
This method works better with manifold meshes. The size of the bones also influences the result: bigger bones will attract more vertices. Don't forget that one can add remaining parts by hand later by using vertex groups.
I tested user14351's method and it works for your model (except for the teeth) . You need to add a subsurf modifier before parenting the armature to the mesh.
