(Encore episode) The mirror self-recognition test has been around for decades. Only a few species have what it takes to recognize themselves, while others learn to use mirrors as tools. NPR science correspondent Nell Greenfieldboyce talks us through mirror self-recognition and why Maddie's dog is staring at her. For more science reporting and stories, follow Nell on twitter @nell_sci_NPR. And, as always, email us at shortwave@npr.org.