 The album includes ballads and acoustic songs featuring extensive use of guitar and piano . The U2 @-@ esque " epic rock " of the album 's opening track " Politik " , the piano @-@ driven " Clocks " , the loud guitars of " A Whisper " and the Crowded House @-@ inspired guitar in " Warning Sign " were seen as an extension of the band 's musical range . Chris Martin has stated that the album 's title track is an homage to American singer @-@ songwriter Johnny Cash , whom he considered one of " the greatest ... men with just guitars " . 
