It is a fair question, not a philosophical one but a physiological or medical curiosity we wish to answer in relation to how healing is achieved.
Perhaps, you may not have encountered the question before. Or you may not think of it as important or worth considering. For why should we bother how we smile or whether it comes from the heart, the head or the kidneys, for that matter. Maybe the whole body “smiles” and feels the happiness all over. It just so happens that the lips manifest that happiness just as the tears from our eyes manifests our sorrow.