Many educators have used Algorithm Visualization (AV) to teach students of computer science about how computer algorithms work. Our study sheds light on two important questions: (a) How do people conceptualize algorithm animations in the first place; and (b) To what extent do such visualizations accord with AV software. In the first half of this study, pairs of graduate students in computer science were asked to construct animations for a simple sort (bubble sort) using ordinary art materials. In the second half, they implemented a bubble sort visualization using Mukherjea & Stasko [ l] interactive AV program, LENS, which animates any sorting algorithm. The way in which pairs visualized the same sort differed tremendously from each other and did not accord completely with the animation language provided by LENS. This paper analyzes those differences by a detailed examination of the semantics of the human visualizations, the algorithm code, and the LENS AV language.