In recent years, students in our introductory object-oriented programming course have become familiar with Zoom and screen sharing. Leveraging this, we have developed a style of assessment where students submit a recorded screencast of them tracing their submitted programs. We describe the design of the assessment and tracing prompts, and we report on an analysis of 59 submitted student videos. Our findings include common mistakes and aspects of student understanding that were expressed in the video but not in the text and code submitted by students. For example, we observed different strategies that yielded the same correct trace of a loop, as well as incorrect traces of students’ own correct recursive programs. These guide us towards ways to refine the assessment and prompts in future iterations.