The design of experimental ecological fieldwork is difficult to teach to classes, particularly when protocols for data collection are normally carefully controlled by the class organiser. Normally, reinforcement of the some problems of experimental design such as the avoidance of pseudoreplication and appropriate sampling techniques does not occur until students conduct individual project work. Here, a practical session is described where students collect data on the vigilance of grazing animals, following a protocol that allows them to make typical mistakes in experimental design that are then discussed in class. Being able to explore these problems with a group of students could give valuable training in experimental design before students conduct individual projects, and therefore would be recommended as early training on fieldcourses, or as a preliminary exercise for honours projects.