Exams are a form of assessment that is ubiquitous in college STEM classrooms yet is infrequently studied from the experiential perspectives of instructors or students. To better understand the forms, methods, and experiences of college STEM exams, we conducted survey-based research with instructors in anatomy and physiology courses, a well-defined and popular subset of STEM courses. We used a combination of qualitative and quantitative questions to learn about exam methods in the classrooms of 63 instructors, through which many thousands of exam-student interactions happen each year. Our data suggest that exams are a significant, possibly onerous undertaking for instructors, including many forms of optional support for students, and that they have an outsized impact on students' grades (and thus their persistence towards STEM careers). Instructors' survey responses imply that sustainability of the methods they use for assessment is a key and pressing concern in their professional lives. This need for sustainability may lead to tradeoffs that impact students, such as decreasing the transparency of the exam experience, sometimes to an extent that exams may be perceived as highly secretive. The feasibility of instructors accommodating students' absences and of students challenging instructors' grading are discussed as exemplars of the complex communication that, for better or worse, is central to student-instructor relationships and the outcomes of STEM classrooms.