This case study reports on how students, working collaboratively, interpret and construct a written report of the events described in animated educational software. The analysis is based on video recordings of two upper-secondary-school students while they are endeavouring to construe an animated sequence of the mouldering process. How the students grammatically construct their written account by means of available semiotic resources (i.e., animation and educational text) provided by the software is investigated. The results show that attentionally detected features of the animation take the role of active subjects in the students' description of the animated phenomena. When framing their sentences, the students derive noun phrases from animated active subjects and from the educational text. In the students' efforts to express themselves in their own words, they use verbs that differ from the educational text. These two actions together contribute to giving the students' description of the process a character of a non-scientific explanation. Lacking relevant subject matter knowledge, the students cannot judge whether they have given an adequate account or not. The only way that the students have to appraise their written report is to check if it is grammatically correct. It is concluded that it is essential to consider both cultural and semiotic processes when designing technology-supported educational approaches to the teaching of scientific concepts.