While it is common for teachers to focus on learners' errors in the EFL classroom, little attention is given to the "errors" that native English speakers make in their mother tongue. This paper reports on a study to assess the reaction of Japanese university students to an activity that primarily required identifying "ungrammatical" forms in audio clips of English NSs. The results of a post-activity questionnaire suggest that exposure to this particular feature of spoken language may make students less inhibited about making errors and thus help to overcome their reticence to speak in class. These initial findings were confirmed in a follow-up study conducted at a second Japanese university.