Ed Sheeran sings snippets of "Thinking out loud"

'Shape of You' singer Ed Sheeran picked up a guitar and briefly sang for the Manhattan courtroom on Thursday during the trial settling the case of whether the singer's 'Thinking Out Loud' plagiarized the Marvin Gaye hit "Let's Get It On".

Sheeran performed a bit of what he said was the first version of "Thinking Out Loud," as he and co-writer Amy Wadge developed it together at his home in England. The song's hook lyric was then -- as he sang it -- "I'm singing out now," according to musical testimony reported by ABC News.

According to Variety, Sheeran testified, "When I write vocal melodies, it's like phonetics," and showed "singing out now" became "thinking out loud."

Under examination from his attorney, Ilene Farkas, Sheeran described the composing of the song in 2014 as a quick and not deeply thought-out process. He said he had just emerged from the shower when he heard Wadge playing guitar chords and was drawn to join her to start developing them into a song. "I remember thinking we have to do something with that," he said, according to ABC. "Amy definitely started strumming the chords..." Of the process, which Sheeran said took "really not that long," he added, "We sat guitar to guitar. We wrote together quite a lot."

As reported by Variety, in contention in the trial is the plaintiffs' assertion that "Let's Get It On" and "Thinking Out Loud" are rooted in the same four chords.

Earlier in the day, the defence played in court a video from a British television show that was meant to demonstrate that the same four chords could be the basis of an infinite number of songs.

The video was played during Sheeran's attorneys' cross-examination of Dr. Alexander Stewart, a musicologist brought in by the plaintiffs, who on Wednesday has testified that the two songs have a substantial similarity.

The Court adjourned in the midst of Sheeran's testimony, and the trial will return on Monday with the singer back on the stand to undergo cross-examination.

Sheeran, Warner Music Group and Sony Music Publishing are being sued by three heirs of songwriter Ed Townsend, who is the credited co-writer with Gaye on 1973's "Let's Get It On."