The line at the start of the chorus is "but you know nothing is as silent" not "but you know nothing is outside", which makes no sense because some things are outside, just look out the window and anything you see is probably outside. Also, it's not cail yard, it's Kailyard (the kailyard school of Scottish Fiction ) here's alink to it's Wiki page http://en.wikipedia.org/wiki/Kailyard_school
The line at the start of the chorus is "but you know nothing is as silent" not "but you know nothing is outside", which makes no sense because some things are outside, just look out the window and anything you see is probably outside. Also, it's not cail yard, it's Kailyard (the kailyard school of Scottish Fiction ) here's alink to it's Wiki page http://en.wikipedia.org/wiki/Kailyard_school