This should be: `StdMeshSkeleton& GetSkeleton() { return *Skeleton; }`. The idea is to have a method just like the const version of `GetSkeleton()` with the same name. This works because one method is const and the other is not const. The compiler calls the right version depending on whether the object it is called on is const or not. This allows to obtain a non-const skeleton if you have a non-const mesh, and "only" a const skeleton if you have a const mesh.

The way it is now the method `GetSkeleton()` is useless in the sense that one could always use `GetSkeletonPtr()` instead, and can therefore obtain a skeleton that can be modified even if the mesh itself is const.