# module singleton methods included in a class do not respond to Class.method call
# NoMethodError is raised
module Bla
  def self.bla
    puts 'hello bla'
  end
end

class Foo
  include Bla
  def self.blaf
    puts 'hello blaf'
  end
end

Foo.blaf # => 'hello blaf'
Foo.bla # => undefined method `bla' for Foo:Class (NoMethodError)