Three-dimensional synthetic worlds introduce possibilities for nonverbal communication in computer-mediated language learning. This paper presents an original methodological framework for the study of multimodal communication in such worlds. It offers a classification of verbal and nonverbal communication acts in the synthetic world Second Life and outlines relationships between the different types of acts that are built into the environment. The paper highlights some of the differences between the synthetic world's communication modes and those of face-to-face communication and exemplifies the interest of these for communication within a pedagogical context. We report on the application of the methodological framework to a course in Second Life which formed part of the European project ARCHI21. This course, for Architecture students, adopted a Content and Learning Integrated Learning approach (CLIL). The languages studied were French and English. A collaborative building activity in the students L2 is considered, using a method designed to organise the data collected in screen recordings and to code and transcribe the multimodal acts. We explore whether nonverbal communication acts are autonomous in Second Life or whether interaction between synchronous verbal and nonverbal communication exists. Our study describes how the distribution of the verbal and nonverbal modes varied depending on the pre-defined role the student undertook during the activity. We also describe the use of nonverbal communication to overcome verbal miscommunication where direction and orientation were concerned. In addition, we illustrate how nonverbal acts were used to secure the context for deictic references to objects made in the verbal mode. Finally, we discuss the importance of nonverbal and verbal communication modes in the proxemic organisation of students and the impact of proxemic organisation on the quantity of students' verbal production and the topics discussed in this mode. This paper seeks to contribute to some of the methodological reflections needed to better understand the affordances of synthetic worlds, including the verbal and nonverbal communication opportunities Second Life offers, how students use these and their impact on the interaction concerning the task given to students.