Final answer:
Mr. Martin used an old gray-headed negro musician playing a scraped and battered instrument for the arrangement of 'Yesterday'. The unique sound created by this ensemble added character to the song.
Step-by-step explanation:
Mr. Martin used an ensemble composed of an old gray-headed negro playing a scraped and battered instrument for the arrangement of 'Yesterday'. The musician would scrape on two or three strings and accompany the movement of the bow with his head and foot. This ensemble created a unique and rustic sound for the song.