We like to do our trial run around 3 p.m., so that we still have enough time to fix mistakes and patch any holes we find in the prototype. Have everyone pause work and gather around, and then ask the Stitcher to walk through the entire prototype, narrating as he goes. As you go, you should double-check against the storyboard to make sure everything made it into the prototype. The trial run is also a great time to revisit your sprint questions. It’s one last check to make sure your prototype will help you get answers.