The significance of errors in explicating Second Language Acquisition (SLA) processes led to the growth of error analysis in the 1970s which has since maintained its prominence in English as a second/foreign language (L2) research. However, one problem with this research is errors are often taken for granted, without problematising them and their identification. Against this background, the present study aimed to: (a) measure L2 English teachers' ability to interpret L2 learner intentions in idiosyncratic expressions, and (b) bring to light factors that facilitate error identification. Findings show that: (1) there is a significant difference between L2 students' intentions and teachers' interpretations of those intentions; and (2) L2 English teachers' knowledge of students' L1 is not an advantage in error detection. Teacher interview data were drawn on to explicate text interpretation, reconstruction and error identification, suggesting implications for L2 research and pedagogy.