Groups approach the Trolley exercise in many different ways. The key thing of concern to you is that people behave in a safe way and that they do better and better each of the three times they try. This means you can alter the time or the rules in a flexible way, to guarantee progress. In the slides on the 1st Try there is no sounds. On the 2nd Try there is only no understandable words. On the 3rd Try they can experiment and talk to each other.
See The Systems Thinking Playbook , page 31, Section II for another version of this exercise.