The seminal work by Ericsson and Simon established verbal reports as a genuine way to get a glimpse into the “black box” of the workings of the human mind, and it is now recognised as a method of value in the pursuit of new knowledge relating to, for instance, learner strategies, cognitive strategies, human-computer interaction, and functionality of software and hardware. The present paper presents a think-aloud study (concurrent verbal report) which was conducted with university students of English as a Foreign Language, who were using a CALL program to learn English syntax. The students were asked to verbalise their thoughts while conducting the task of parsing sentences and building tree diagrams on the computer. The computer program Visual Interactive Syntax learning (VISL) is operational in fifteen different languages ranging from English, French, and German to Arabic, Danish, Dutch, Latin, Greek, and Japanese, and allows the students to learn and work with syntax in their own speed. VISL contains a ...