The study combines Science and Technology Studies interest on materiality with knowledge creation and transmission, typical concepts of Practicebased Studies. Knowledge is meant here as a process of socio-material connections. The analysis focuses on a “typical” place of knowledge transmission such as a training course, namely on safety connected to wild fire-fighting. The discursive mobilization of some safety objects during the training makes evident the conflicting positions between the Fire-Brigade and volunteers on safety and fire-fighting. In literature this communicative split is often considered as an obstacle to the development of common understanding and coordinated action. A deeper analysis of discursive interactions highlights the role that dissonance and conflict may play in softening the boundaries between communities of practice and in producing knowledge. The aim of the contribution is also to underline that knowledge not only is an effect of alignment but also of dis-alignment of human and non-human actors.