This paper examines how unplanned vocabulary work arises out of students' talk. Furthermore, we show how the teacher and students jointly contribute towards the ensuing teaching trajectories, whereby the vocabulary items are turned into 'teachables', i.e. interactionally emergent objects of explicit teaching. In doing so, we also explore what aspects of vocabulary knowledge are targeted. This collection-based study uses conversation analysis to examine video recordings of fairly advanced heritage speakers of English from English mother tongue instruction classes in Sweden. The analyses reveal a variety of ways in which the teaching trajectories arise: the teacher's "substitution requests" for a more appropriate word; a student's "naming" and "word-confirmation requests"; the teacher's or a student's "translation" and "meaning requests." A third of these requests were initiated by a student. The trajectories then developed collaboratively and were tailored to the local context to address issues of "meaning," "form" and "use." Establishing the meaning of a word frequently involved (and could combine) requesting/providing, e.g., definitions and translations. Form could be targeted by carefully enunciating topicalised lexis or writing it on the board, and vocabulary use was typically elaborated by contextualising words and sometimes by exploring collocations.