The exact size and placement of the holes on each sheet, and the spacing between the sheets, has a predictable effect on incoming sound waves.

BBC: Acoustic 'cloaking device' shields objects from sound

When pressed to say whether more quantitative easing would have the desired effect, the incoming governor said, matter-of-factly, that Bank of Canada research had concluded the policy was having diminishing returns, especially in the US. He added this was "not surprising".

BBC: Governor Carney: Same remit, new ambition