Mastery comes in many forms.
Each spring, Oxy seniors produce a senior comprehensive (or comp)—create a project or paper or take a test that demonstrates mastery of their chosen field. It's a major production: studio art majors take over Weingart Galley for the senior art show. Film students showcase their work at a film festival that fills Thorne Hall.
Music majors appear in recitals that feature their vocal, instrumental and compositional skills. East Asian studies majors deliver oral presentations in Chinese and Japanese. Seniors in other departments deliver talks or papers on everything from "Enlightenment Transformation of the Maja: Francisco Goya's Los Caprichos and Fernando de Rojas' La Celestina" to "Afghanistan, Pakistan, Pashtunistan: A Study of of Ethnic Nationalism in Post-Colonial Central Asia."
In many cases, comps draw on work seniors carried out during study abroad or during their collaboration with a faculty member in the undergraduate research program. (And most of the departmental comps presentations provide cookies, too.)