must declare a body because it is not marked abstract, extern, or partial

This error is not always giving the correct message

consider:

class Animal

    {

         Animal();

    }

  

this will raise the above error

but this :

     partial class Animal

    {

        partial Animal();

    }

    partial class Animal

    {

        Animal() { }

    }

wont help 

why? partial procedures need to return void