Frances and Edith have idiosyncratic licking problems, too. (Frances obsessively licks a hot spot on her foot and Edith obsessively licks Frances's face.) DISCLAIMER FROM DREWTOOTHPASTE (author of video): "The licking is not a serious medical problem. Charles is under regular veterinary care, and was not harmed during the making of the video. He is just a weird dog." In other words, Charles does not do this all the time. Evidently he is stimulated by the sight of something (tasty treats?) outside the frame.