Up to mid-1965, most of the songs the Rolling Stones had covered had been blues, R&B, and rock'n'roll in nature. With the Out of Our Heads album, however, contemporary soul songs came to dominate their cover repertoire, though this was at the very time when original material was finally starting to become a major part of the Rolling Stones' recorded work. One of the more popular soul covers they did on the album was of "Mercy Mercy," which had been a #35 hit for co-composer Don Covay in late 1964. In its original version, "Mercy Mercy" was an excellent soul tune with a gospel overlay in the pleading tone of the lyrics, with deft Curtis Mayfield-influenced guitar picking by young session man Jimi Hendrix. The Stones' cover really upped the guitar wattage, as heard in the memorable opening section of interwoven guitars and, more particularly, in the booming low fuzz guitar riffs that underpin the verses. There were more backup harmonies than many people realize on the Rolling Stones' records, and "Mercy Mercy" makes good use of high ones during the urgent choruses. Mick Jagger was at this point gaining confidence as a soul-rock vocalist, and does a good job of pleading his case without sounding like he's about to stoop to begging. Especially good are the points at the end of the bridge; on one pass, all the instruments drop out to leave Jagger to declare his determination sans backing, while at another the group leaps into falsetto harmonies to sing "please don't say we're through!" "Mercy Mercy" is a good performance of a song that's catchier and more melodically sophisticated than many of the more rudimentary, bluesy tunes the Stones covered in their slightly earlier recordings. A good number of others have done the song, including Gary U.S. Bonds, the Remains, the 13th Floor Elevators, Booker T. & the MGs (in an instrumental version), Wilson Pickett, and Alan Price.