In this paper, we look at how prosody can be used to automatically distinguish between different dialogue act functions and how it determines degree of speaker incipiency. We focus on the different uses of `yeah'. Firstly, we investigate ambiguous dialogue act functions of `yeah': `yeah' is most frequently used as a backchannel or an assessment. Secondly, we look at the degree of speakership incipiency of `yeah': some `yeah' items display a greater intent of the speaker to take the floor. Classification experiments with decision trees were performed to assess the role of prosody: we found that prosody indeed plays a role in disambiguating dialogue act functions and in determining degree of speaker incipiency of `yeah'.