This study, part of a larger linguistic ethnographic enquiry carried out in two primary school classrooms in Flanders and the Netherlands, sheds light on the perils faced by the ethnographer caught between pupils' inventiveness and his own ethnographic naivety when dealing with these pupils' ethnolinguistic identity construction. The study first focuses on a classroom interaction set up by the teacher, who--because of the presence of the classroom ethnographer--wishes to construct one pupil's identity accordingly to a presupposed yet untapped ethnolinguistic affiliation that matches the ethnographer's ethnic background. Second, the study takes a reflexive peak at the ethnographer's own performance and at how he stumbles into a trap set up by two multilingual pupils through emblematic language use. The article concludes by drawing a number of considerations with regard to linguistic ethnography and the interface between the ethnographer, the object of knowing and the known. It advocates for an interest in the mundane construction of sameness rather than solely on its ruptures.