Visit the official site: http://itv.com/xfactor 4th Impact perform their mentor Cheryl's own song - the Girls Aloud hit Sound of the Underground - along with Shirley Ellis' Clapping Song. SUBSCRIBE: http://bit.ly/TXFSub Facebook: http://bit.ly/TXFFB Twitter: http://bit.ly/TXFTwi Download The X Factor mobile app: http://bit.ly/TXFapp Watch full episodes on ITV Player (UK ONLY): http://www.itv.com/itvplayer