As algorithms have been seen to be hard to teach and learn, teachers have tried to look for help in algorithm animation. While the effect of algorithm animation on learning has been studied, but not reliably evidenced, this study tries to approach the problem from a different perspective. Sixty hours of assignment sessions in an introductory programming course were observed to determine the kind of demonstration and explaining strategies teachers and students tend to use. The results show that although the variation of different visualisation types is large, there are certain common properties describing the explanation of the programs. Guidelines for demonstration tools are presented based on the results.