Sounds like h-nmm, hh-aaaah, hn-hn, unkay, nyeah, ummum, uuh and um-hmuh-hm, occur in American English conversation but have thus far escaped systematic study. This article reports a study of both the forms and functions of these items, together with related tokens such as um and uh-huh, in a corpus of American English conversations. These sounds appear not to be lexical, in that they are productively generated rather than finite in number, and in that the sound-meaning mapping is compositional rather than arbitrary. This implies that English bears within it a small specialized sub-language which follows different rules from the language as a whole. This functions supported by this sub-language complement those of main-channel English; they include lowoverhead turn-taking control, negotiation of agreement, signaling of recognition and comprehension, management of interpersonal relations such as control and affiliation, and the expression of emotion, attitude, and affect.