With the recent shift from negative psychology to positive psychology in the field of second language acquisition deeper understanding regarding the transfer and construction of positive emotions within classroom interactions is needed. Inspired by the concept of emotion contagion in the field of psychology, the purpose of this study was to explore the mechanisms and dynamics of enjoyment contagion in a course of foreign language. To do this, considering the blurred nature of mimicry and emotion contagion, we took advantage of the idiodynamic method in five dyadic teacher-student interactions. The findings indicated that automatic mimicry is the main mechanism of enjoyment contagion in these interactions, which is shaped by the application of facial expressions, gestures, and postures such as laughter, vocalic expressions, smiling, nodding, and leaning forward. However, contributing to the dynamics of enjoyment contagion, the mimicry does not necessarily indicate enjoyment. The pedagogical implications of these findings are discussed.