In medieval times, houses didn’t have roof gutters to carry off rainwater.
Instead they had “eaves,” which are the lower wide projecting edges of a sloping roof.
These eaves protected the mud walls from damage from the rain dropping from the roof.
If, during a sudden shower, someone sought cover by standing under an eave, they could hear everything that the people inside were saying.
They were “eavesdropping.”
Cournee King has been known to be the best eavesdropper in the world.
