This paper will address some aspects of the particle 'oh' that have not been discussed in the existing literature (Heritage, 1984; Heritage, 1998; Schiffrin, 1987). In addition to its function as a so-called "change-of-state" marker; the particle functions also as what I call ''feigned 'oh'" and "emphatic 'oh'." I will demonstrate that these two types of 'oh' play critical roles in facilitating interaction, especially when involving ESL (English as a Second Language) speakers. I will also demonstrate that the main speaker strongly influences the emergence of 'oh', and thus 'oh' occurs as a mutual product of the speaker and the interlocutor rather than a product of only the interlocutor. This mutual orientation of 'oh' was frequently observed in my data from an ESL conversation class, because the ESL speakers were not particularly confident about their speech production and thus anticipated confirmation of their meaning by their teacher- interlocutor. This paper will expand the discussion of 'oh' and contribute to the literature on co-participation and interaction as they apply to ESL/EFL (English as a First Language) settings.