In early 1968, The Beatles were between albums and about to embark on an extended retreat at the compound of the Maharishi Mahesh Yogi in Rishikesh, in the Indian foothills of the Himalayas. They weren’t obligated to record anything during this period, as their soundtrack album Magical Mystery Tour had just been released, and the scheduling of their output had become more scattergun since they quit touring in 1966.

Still, the film studio United Artists was asking for more music to use on their upcoming Beatles animated feature Yellow Submarine. The band felt like releasing a single to fill some of the gap between album releases they were expecting to occur because of their time away in India.

And so, they headed back into the studio for three days across the first half of February 1968 and duly came out with three songs. The liveliest and most adventurous of which wasn’t the single ‘Lady Madonna’ or its B-side ‘The Inner Light’, but a song that didn’t surface until almost a year.

‘Hey Bulldog’ was some of the most fun John Lennon ever had with a Beatles song. It feels at odds with most of the compositions he contributed to the group from 1967 onwards, many of which either exposed his emotional state to breaking point or presented him as jaded and disinterested. In more recent evaluations of The Beatles’ song catalogue, it’s rightly been afforded classic status, including by Nirvana drummer and Foo Fighters frontman Dave Grohl.

The track is underpinned by a hook that wouldn’t be out of place in the theme of a detective show, while Lennon and McCartney revel in spitting out close vocal harmonies with the sass of an upbeat soul number. Its lyrics sound like gibberish but contain enough lines of genuine poetry to form a compelling picture of a person outwardly sure of themselves but wracked with internal insecurities.

So what about the “woofing”?

Yet the element of ‘Hey Bulldog’ that really sets it apart is the barking of a dog, which can be heard during the song’s coda. The first of the barks is an especially convincing low-pitched “Woof!” before Lennon asks in a faux-American accent, “What do you say?”. The “Woof!” is repeated, and Lennon says, “You know any more?”. In response comes a higher-pitched yowl, followed by a bark that sounds like it belongs to a smaller dog than the previous two barks. Lennon then emits a signature voicebox-shredding scream, and he and McCartney exchange a fast-paced dialogue of nonsense as the song fades out.

The question remains: who brought their dog into the studio to record the barking? The initial barks, in particular, sound like they couldn’t have come from a person. But they did.

McCartney later confirmed that he was the one behind the dog noises on the track during a 1990s interview for the band’s Anthology project. Listening to the song in real-time, McCartney said during the coda, “I start going “Ruff!”, and I start being a dog.”

He explains that this was a spontaneous ad-lib during a live take of the song, in response to Lennon asking, “What’s that boy?” as if he was talking to a dog.

What followed was just as spontaneous and was originally meant to be cut from the final master of the recording until the group decided they thought it was worth keeping. “I think my dog impression is terrific,” McCartney reasoned in his interview. We heartily agree.