Software visualization is nifty stuff; but is it the powerful cognitive tool it is often assumed to be? This chapter attempts to moderate the understandable enthusiasm for software visualization and to raise some of the questions for which the discipline doesn't yet have answers. The chapter is structured as a list of questions with discussion. The questions are not a comprehensive analysis of cognitive challenges in software visualization. Rather, the chapter attempts to provide a list sufficiently provocative to give designers pause, in order: (a) to establish that good software visualization isn't simply a matter of mimicking paper-based tasks or doing what is technically easy---and certainly isn't `solved' yet; but also (b) even simple tools can improve software comprehension, if they're the right ones.

We give an overview of rules and techniques to create a good algorithm animation, with emphasis on animations that would be used when teaching algorithms. In this context, we propose that animations should in particular emphasize the visualization of correctness invariants and the complexity of the algorithms. This implies that writing a good animation must be more than just showing the graphically enhanced runtime debugging provided by most common animation systems; instead, each animation must be individually designed and programmed.