Diagnostic work in trauma teams is critical for the patient's condition and for the possibility of survival. It is a difficult situation to train due to the inherently unpredictable and time-critical practice when an injured patient presents in the Emergency Room (ER). Different types of simulations have been developed for specialized training of specific skills and on contribution to teamwork, but there are hardly any studies reporting on opportunities to train realistic, multidisciplinary collaboration and communicative skills in such time-critical settings. In this article we report on a collaboration-oriented simulation where a trauma team performs diagnostic work: examining a patient in an ER at a hospital. The setting studied is arranged as a design experiment and video data constitute the basis for our interaction analysis. Our main finding is that highly-specialized simulations are useful as an arena for communication training among trauma team members. Doctors and nurses manage to make the simulated representations relevant in their talk, share medical observations and examinations, and consecutively include these findings into their collaborative diagnostic trajectory.