Calls to immerse students in the sensemaking practices of science recommend that students propose ideas and work together to construct explanations as well as drive the evaluation and decision-making around classroom knowledge-building. In other words, they should be participating with epistemic agency. Part of the teaching work of supporting student sensemaking, therefore, is to intentionally open up space for student contributions and negotiations during sensemaking. The type of space that is opened up for students' sensemaking is highly dependent on teachers' choices and interpretations of student contributions. Accordingly, this paper leverages a teacher noticing framework to begin to characterize the teacher noticing and decision-making involved in supporting students' epistemic agency while teaching. Using a novel point-of-view video collection methodology, we asked two teachers to identify moments while teaching in which they were making a decision about how to open up or close down space for students' epistemic agency. We found that both teachers attended similarly to the "disciplinary substance" of students' ideas; the "epistemic nature" of students' ideas; students' "epistemic stance or orientation" during participation; and students' overall "degree of engagement." Teachers' responses to students varied across pedagogical phenomena, and they also varied in their effectiveness. These variations were related to each teacher's conception of epistemic agency. We propose that attention to the "epistemic nature" of students' responses and to students' "epistemic stance or orientation" may be especially important foci of teacher attention for supporting students' epistemic agency.