Mathematics curricula increasingly emphasise the importance of mathematical communication. Students are seen as progressing from the use of a more informal or everyday form of communication to a more mathematical approach. There have, however, been very few studies of how mathematicians actually talk about mathematics. This paper reports analysis of mathematicians' talk in the context of a live, unscripted radio discussion between three mathematicians and the series presenter. Analysis draws on discursive psychology and highlights an interpretative repertoire drawn on by participants that constructs mathematics as expert practice. Mathematicians' expert ways of seeing and thinking are contrasted with the more everyday perspective of "most people". The findings raise questions about what it means to learn to talk about academic mathematics in a school setting. (Contains 2 notes.)