I often find that running a retrospective, the routine part of it often warms up people. However the real value is when I ask the question “ok now that is all in the open, how are you really feeling?” This I have seen is often taken by surprise and the value of the conversation now really starts to flow. It is no longer trottled by preconditioning. It’s amazing to see how people much people do really want to open up.
Also attached a few interesting images from my previous retrospectives gamifying the session.