The beak was held in front of the doctor's nose by straps. There were two holes in the mask, filled with glass at eye level, so that the doctor could see properly. The mask had two smaller holes for the doctor to breathe. It was a type of respirator which was often filled with strong, nice smelling things. Dried flowers (such as roses and carnations), herbs (such as mint), spices, camphor or a vinegar sponge could all be placed in the beak. The mask was supposed to keep away bad smells. At that time, it was thought that bad smells caused infection. Doctors believed the herbs would take away the "evil" smells of the plague and stop them from getting it.