The typical mask had glass openings for the eyes and a curved beak shaped like a bird's beak with straps that held the beak in front of the doctor's nose.[6] The mask had two small nose holes and was a type of respirator which contained aromatic items.[7] The beak could hold dried flowers (including roses and carnations), herbs (including lavender and peppermint), camphor, or a vinegar sponge,[8][9] as well as juniper berry, ambergris, cloves, labdanum, myrrh, and storax.[10] The purpose of the mask was to keep away bad smells, known as miasma, which were thought to be the principal cause of the disease.[11] Doctors believed the herbs would counter the "evil" smells of the plague and prevent them from becoming infected.[12]