Which animal features in the Sherlock Holmes story, "The Adventure of the Blue Carbuncle"?

This is the seventh story of twelve in the collection "The Adventures of Sherlock Holmes" by Arthur Conan Doyle.

Shortly before Christmas it is reported that a near-priceless gemstone, the "Blue Carbuncle", has been stolen from the London hotel suite of the Countess of Morcar. The police arrest John Horner, a plumber with a criminal record who was in the Countess's room doing some repair work. But it is a set-up.

A doorman speaks to Sherlock Homes about two lost items that he would like to return to their owner: a hat and a Christmas goose. Holmes takes the hat to try to find the owner and tells the doorman to keep the goose. The doorman returns excited, carrying the stolen gem, and reports that he had found it inside the goose. Holmes tracks down the owner of the hat (who knew nothing about the gem) and questions him about the origin of the goose. The trail leads via a London pub and a Covent Garden dealer to the South London breeder. Along the way, as he expected, Holmes runs into the other person trying to find the valuable goose: the original gem thief. It is the head attendant at the hotel where the gem was stolen. Of course, this man was in league with the Countess’s maid and had set up the framing of the plumber: mystery solved.

What is striking to a modern reader is that, in 1892, the standard Christmas meal featured not turkey or chicken, but goose. It is also remarkable the extent to which poultry was produced and distributed in urban areas.