In front of every Dementor, Narcissa could see something she could only interpret as cold air in front of their mouths. Rather than it looking like the moisture from one's breath on a cold morning, this had the look that it was constantly being sucked in. None of the Dementors seemed to notice them, judging from their faces and how their "breath" seemed to be at a small rate. I really don't want to see what it looks like when they are sucking on people's happiness with these spectacles...