Hi, as this is an infrequent cough, it's unlikley to be anything serious. It is possible for dogs as well as cats to get hair in their throat if they are washing themselves alot due to itchy skin- so it would be worth checking for skin problems. It could be a cough caused by an allergy or bronchitis triggered by something occasional. Coughing can also be a sign of heart or lung disease or anything causing inflammation or obstruction in the throat, but in these cases it would be more continual or at least daily. Next time you are at the vet clinic ask your vet to check the chest and throat in particular, but don't worry in the meantime.