Why did Led Zepplin name their song "Black Dog"?

The title of the song Black Dog was inspired by a stray labradour that wandered in and out of the Headley Grange studio where the band was recording Led Zeppelin IV at the time.

https://iloveclassicrock.com/how-led-zeppelin-wrote-black-dog/

Led Zeppelin's fourth album was released on November 8, 1971. There was no indication of the band's name on the original packaging, and the title of the album was given as four symbols - . It is variously referred to as The Unnamed Album, Untitled, Led Zeppelin IV, Zoso, Runes, Sticks or Four Symbols. In an interview with Rolling Stone magazine in 2005, Plant said that it is simply called the fourth album.

The album included hard rock, such as "Black Dog" (supposedly titled in tribute to a dog which loitered around the recording studio) along with gentler, acoustic folk-style tracks such as "Going to California" (a tribute to Joni Mitchell).
https://en.wikipedia.org/wiki/Led_zeppelin

Jimmy Page has said that Black Dog is Zep's "answer" to Fleetwood Mac's "Oh Well."