This qualitative case study delved into students' understanding and positioning while they participated in solving an authentic, conceptually-based problem in a high-school chemistry class. Verbal and nonverbal cues, particularly gestures, offered broader awareness of students' engagement in sensemaking during the learning experience. The chemistry classroom emerged as a dynamic space where intricate scientific thinking unfolded during this experience, and our embodied, multimodal analysis focused on unraveling this complexity. Our analysis determined the ways that various features of the contextual configuration--the intersection of different semiotic fields in the social setting--affected student thinking and participation. For example, the lack of specific reference to semiotic resources and the lack of attention to a key gesture influenced the way ideas evolved in the solution generation phase. The analysis also revealed the teacher's impact on the contextual configuration at critical junctures, including her influence on the use of semiotic resources and on student positioning. Finally, the embodied and multimodal analysis provided insights into the affordances and constraints of the activity structure and modes of communication on student's involvement in scientific practices. These insights highlighted the importance of educators recognizing diverse forms of student expression, including gestures, as essential for nurturing scientific sensemaking and supporting students in utilizing different modalities productively. Our approach can assist researchers in holistically investigating pedagogical strategies that can facilitate reform-based science teaching. It can also assist teachers in fostering effective communication--both verbal and non-verbal, while simultaneously guiding positioning within and between student groups, establishing an environment conducive to equitable sensemaking.