The art of the yarn bomb

Balls of yarn sit on a bench during a yarn bombing in Martin Place, Sydney, Australia.  (Tracey Nearmy / EPA)

A woman puts knitted yarn on a street pole during a yarn bombing in Martin Place, Sydney, Australia.  (Tracey Nearmy / EPA)

A bench tangled up in yarn during a yarn bombing in Martin Place, Sydney, Australia.  (Tracey Nearmy / EPA)

A yarn bomb installation in Vancouver, Canada.  (Jeff Christenson / Associated Press)