I've recently been facilitating retros for a team where safety has been exceptionally high. As a learning retrospective facilitator, this situation is interesting for me because it makes me want to explore dynamics other than safety. The Agile Retrospectives book has a few activities that I find quite useful. I recently used Explorers, Sailors, Vacationers, Prisoners (ESVP) as a start up activity and skipped the safety check. Its a nice tool to understand people's attitude to the retro.I run it a little differently from the way its described in the book.
Very simply,I choose to keep the activity anonymous and make it more visual. I usually start off by preparing a flipchart/ board with some pictures drawn on them.
I usually then ask the participants to write an "E"/"S"/"V"/"P" on their stickies, fold it up and give it to me (the facilitator). I like doing this, because it keeps their identities secret and yet gives an indication of the general mood of the group.
Obviously there are possible antipatterns to this activity and the book does mention some mitigation strategies that I wont mention here. The couple of runs we did with this were quite successful and very effectively set the tone for the retros. I do recommend this as a "try".
A week back I also tried an absolute mindless and unconventional activity to start a retro (again with a team demonstrating high safety) and conducted a rather funny quiz to get the energy and enthusiasm flowing. The questions were really odd (taken from a slideshow I found somewhere) - eg "How many years did the 100 year war last"? and "Where do Chinese gooseberries come from?". The intention was to get people into a happy enthusiastic mood, and it helped. I know that this is rather a strange beginning to a retro, but at the same time, in the situation and given the dynamics of the team, perhaps the right way to set the tone for the exercises to follow.