function mobkit.before_shutdown() -- called by minetest.register_on_shutdown()
    local objects = minetest.get_objects_inside_radius({x=0, y=0, z=0}, 31000)
    for _, obj in ipairs(objects) do
            local self = obj:get_luaentity()
            local n = self.name
            if type(minetest.registered_entities[n].head) == "boolean" then
                    obj:remove()  -- more likely an error happens here
                    self = nil
            end
    end
end