Computer generated animations are resources used to explain how programs are executed in order to clarify the relevant programming concepts. However, whilst trying to understand new programming concepts it is not clear how and when students benefit from an animation if they are using the tool on their own. To clarify the role of an animation tool in the student learning process, six students from an introductory programming course at a Tanzanian university attended three individual sessions. In each session students used a program animation tool to understand a new programming concept, and they were asked to orally describe the animations as they watched them. The authors conducted a qualitative analysis on the video and audio recordings taken when the students described the animations. Through an inductive category generation process, five roles played by the animation tool are identified: no-role or empty, exploratory, confusing, teaching, and evaluating. This classification of roles helps us to understand the potential of animation tools, and suggests that versatile use of an animation tool can enrich the teaching and learning process by diagnosing a student's current learning stage and by engaging the student in the learning activity. (Contains 2 tables and 3 figures.)