Certified nursing assistants are usually required to meet certain physical expectations such as lifting and bending requirements and the stamina to last long shifts on their feet. In addition, their job description includes certain tasks that are sometimes unpleasant or uncomfortable to some people, such as working with sick or infected persons or cleaning up stool or vomit. The CNA can certainly refuse any task that they feel incompetent to perform and should request supervision or training, and all tasks that do not fall within the scope of practice for their certification requirements such as administering medications or doing invasive procedures, for example.