A few minutes later we heard them shouting back and forth. I looked at Adam with a cocked eyebrow and asked him, "Are they trying to talk through their walls?" We told them to be quiet and forgot about it.
Just now, hours later, they are in their rooms supposedly getting ready for bed. Adam and I are in the living room and we can hear muffled echos. We put two and two together and crawled over to the floor vent. We could hear their conversation all the way on the other side of the house, coming up through the vents. They'd been laying on their floors, having "secret" talks through the vents!