One of the main issues in language learning is to find ways to enable learners to interact with the language input in an involved task. Given that computer-based simulation allows learners to interact with visual modes, this article examines how the interaction of students with an online video simulation affects their second language video comprehension and incidental vocabulary learning. Forty-three Arab adult learners were randomly assigned to either an experimental group or a control group. Students in the experimental group (players) participated in a virtual knee surgery simulation by dragging various surgery devices, which were shown in the clip, over the knee of a patient. Those in the control group (viewers) viewed the same video in YouTube and were requested to watch and listen to the video surgery. After the treatments, the students took comprehension and vocabulary recognition tests (image association with words). Results show that the players significantly outperformed the viewers in these two tests. The pedagogical implications of this study suggest that interactivity in language input is crucial in facilitating second language acquisition.