It is obvious that the musician is practising rather than performing, for from time to time the gnarled strain breaks off and, after an interval of indistinct mutterings, recommences.

很明显，音乐家是在练习而不是在表演，因为不时地，粗糙的张力会中断，在一段模糊的喃喃自语之后，又会重新开始。