A 10-week-old abandoned puppy with a secondary tail, in the middle of his head, has been taken in by an animal rescue centre in Missouri.
Staff at Mac's Mission, which is predominantly for animals with special needs, have called the puppy Narwhal.
They had been told there was "no medical need to remove" the extra tail as it caused him no pain, they said.
And the popularity of photos of Narwhal on Facebook had helped raise awareness of the rescue centre's work.
Rochelle Steffen, who runs Mac's Mission, named after a pit-bull terrier she rescued seven and a half years ago, told BBC News Narwhal "is in no pain and plays for hours".
Writing on Facebook, Ms Steffen said Narwhal, named after a species of whale that has a single large "tusk", had visited the vet on Tuesday.
And X-rays had showed his secondary tail, about a third the size of his actual tail, was not connected to anything and served no purpose other than to make him the "coolest puppy ever".
Narwhal is not yet available for adoption as the staff want him to "grow a bit more and truly make sure the tail doesn't become a bother or a problem".
Ms Steffen said Narwhal was one of hundreds of dogs dumped in rural Missouri.
Those taken in by Mac's Mission, who mostly had special needs - deformities, clefts, trauma, "anything major", would otherwise be more likely to be put down, she said, so "there is a great need to give them a chance".
"We give them that chance."
Photos and videos of Narwhal on the centre's Facebook page have gained tens of thousands of "likes" in 24 hours.
And, Ms Steffen says, as its work is "strictly grassroots, through social media" the extra attention "is majorly epic for so many new folks to find out about our awesome little rescue".