Listeners are usually considered recipients in conversational interaction, whose main activity is to take in messages from other speakers. In this view, the listening activity is separate from speaking. Another view is that listeners and speakers are equal co-participants in conversations who construct the talk together. In support of this latter view, one finds a group of vocalisations which are quintessentially listener talk - little conversational objects such as "uh-huh", "oh", "mm", "yeah, right" and "mm-hm". These utterances do not have meanings in a conventional dictionary sense, but are nevertheless loaded with complex and subtle information about the stance listeners take to what they are hearing, information that is gleaned not only from their phonetic form, but also from their complex prosodic shape and their placement and timing within the flow of talk. This book summarises eight of these objects, and explores one, "mm", in depth.