The first time I heard of "Shutter Horns", I was mystified. Inquiry revealed that they were simply a two to three inch extension of the shutter stiles or verticals that protruded from the bottom of the shutter. I suppose that if you flipped a shutter leaf upside down, to could say they were reminiscent of "Horns". It turns out that their purpose is to allow air to flow under the shutter cross-rail and into the house without permitting visiting eyes. And, that's why upper floor windows had louvered shutters... to let old stale air out to be replaced with new fresh air flowing in between the horns. The purpose? Before air conditioning and dehumidifiers, it was the only way to ensure that a house didn't get moldy through the stagnation of the interior air.