While 'flipped' classrooms have been heralded as a valuable tool for student learning, little is known about the process by which students learn from the out-of-class resources. This study investigates 12 undergraduate students' sense-making activities while watching videos about topics in introductory statistics. Analysis of interview data indicated that the students made sense of the videos in very different ways and that the challenges students faced varied widely from person to person. These results highlight the need to take into account the wide variety in students' background knowledge and sense-making practices when creating videos. These results also suggest the importance of structuring students' interactions with videos so that video lectures may become more useful instructional tools for a larger number of students.