The man who came up with the original riff to the song Lose Yourself played the riff on guitar for the High Court at Wellington this afternoon.
A copyright battle over the 2014 National Party campaign ad is in its second day.
The governing party is accused of using an unlicensed version of the hit Eminem song.
Musician and producer Jeff Bass is giving evidence today, and has told how he and Eminem put together the song over a number of months.
Demonstrating the starting riff to the song, Bass accepted an acoustic guitar handed to him by a lawyer and began to play.
He said the song was a "commercial and critical success", hitting number one in the charts and winning Grammys and an Academy Award.
Bass said political parties had asked permission in the past for the song to be used in campaign ads, but they had always been refused.
"We don't want to risk damaging the integrity of Lose Yourself through its association with politics," he said.
He said Eminem Esque was "a blatant rip off of the original" and labelled it "unoriginal".
"I don't care for it."
Eminem Esque is "like Lose Yourself Lite", Bass said.
"Doesn't taste as good though."
He said it didn't "feel like" Lose Yourself, but resembled it.
The defence asked Bass if he agreed the guitar riff was "quite simple", but he said it was not.
The lawyer then read to Bass from an interview he did with Billboard magazine, where he was quoted as saying "It's not that it's so difficult, just two or three chords that just kind of grab your soul and don't let go".
Bass told the court the chords weren't difficult - for someone who had been playing the guitar for 45 years.
Music 'is a close imitation': Court told
A music expert claims that not only did the National Party use music almost identical to Eminem's, but that voice-over of their campaign ad also mimicked Eminem's rap style.
Music expert Dr Andrew Ford today gave evidence via video link from Sydney.
He said the National Party ad "substantially reproduced" Eminem's work, as the track it used, Eminem Esque, was similar in both tone and structure to Eminem's Lose Yourself.
"They have the same staccato use of guitar, identical timbre, and identical chords of D minor and G minor.
"Together they create a sonic bed in Eminem-Esque that is practically identical to Lose Yourself."
Ford then added that Eminem's rap in Lose Yourself started with a "reasonable" tone of voice, and used a rhetorical question.
"The sound and use of the voiceover mimics Eminem's delivery; the sound and tone of delivery, the reasonable voice, the rhetorical question," Ford said.
Lawyer for the National Party, Greg Arthur, then asked the court's permission to play and compare several songs.
Twist and Shout from the Beatle was played, before La Bamba was played and then compared for stylistic similarities.
Kashmir by Led Zeppelin was played to the court, to compare to Eminem's Lose Yourself.
Arthur asked Dr Ford if the similarities could be coincidence.
"It must be possible surely, that of all the tracks in the world, many will share the same beat, tempo, and chord."
Dr Ford laughed before disagreeing.
"I suppose, of all the tracks in the world, there must be some out there.
"If you take all of the information separately, then we're back to my analogy of someone having big ears, it's not very distinctive.
"It's when you put all the information together that it's distinctive."
Arthur continued his line of questioning, putting to Ford that Eminem-Esque didn't have the same features that made Lose Yourself a hit.
But Ford said he believed the track had attempted to include those features.
"It's a close imitation. Close, but pale. It's not as good," Ford said.
"It has all of them, it's just not quite as well achieved.
"I suppose [a coincidence is] possible in a way that a lot of monkeys could eventually type Hamlet.
"But I can't conceive of a way in which Eminem-Esque was conceived without at least close reference to Lose Yourself."
Barbara Zamoyska, who worked as head of film, TV and media for Universal Music Group and was an expert on commercial music licencing said the company would often seek permission from the artist or manager before allowing a song to be used in an advertisement.
"The right piece of music can contribute to the success of a commercial," she said.
"A great track can turn an average commercial into a dynamic one . . . getting the best match between brand and tune is vital."
When the perfect match came along, it was a "rare but visually and aurally exciting" experience.
Zamoyska said the use of a song in an advert would often given the impression an artist was endorsing a certain brand.
The trial is set down for six days.