In the early stages of working with dynamical geometry environments, students make many more mistakes than if they thought out and implemented the same constructions on paper. Most Czech teachers have very little experience of doing geometry using computers. A methodology which could help them to teach students to avoid mistakes dependent on the software used could be very helpful. The main goal of the research was to classify mistakes made in the construction of dynamical figures. The example used was the construction of the figure of "dancing house", which is typical of dynamical constructions. In the paper we cite examples of every type of mistake, documented by screen dumps of the constructions made in Cabri Geometry. (Contains 10 figures.)