receiver -> object[permalink][rdoc]このメソッドオブジェクトのレシーバを返します。
例:
class Foo
  def foo(arg)
    "foo called with arg #{arg}"
  end
end
m = Foo.new.method(:foo) # => #<Method: Foo#foo>
m.receiver # => #<Foo:0x007fb39203eb78>
m.receiver.foo(1) # => "foo called with arg 1"