This article examines the public at a science exhibition or festival and tries to determine whether casual visitors are a means of expanding the audience. According to a Swiss survey of public attitudes towards science (2005), the non-public of a science exhibition or festival is distinguished by demographics such as gender and education (more female and less educated), cultural practices (less frequent) and attitudes towards science (less positive). Considering the Swiss science festival of 2009, casual visitors differ from intentional ones in terms of sociodemographic aspects and scientific cultural practices; on the other hand, casual visitors are close to intentional ones in terms of non-scientific cultural practices and attitudes towards science. Consequently, casual visitors are one way of increasing audiences.