Create a big scale (i.e. a long line) on the floor with masking tape. Mark one end as 'Great' and the other as 'Bad'. Let participants stand on the scale according to their satisfaction with the last iteration. Psychologically, taking a stand physically is different from just saying something. It's more 'real'. You can reuse the scale if you close with activity #44.
Set up a 'retrospective mailbox' at the beginning of the iteration. Whenever something significant happens or someone has an idea for improvement, they write it down and 'post' it. (Alternatively the 'mailbox' can be a visible place. This can spark discussion during the iteration.) Go through the notes and discuss them. A mailbox is great for long iterations and forgetful teams.
Find the source of problems whose origins are hard to pinpoint and lead to endless discussion Source: Henrik Kniberg
Write the problem you want to explore on a sticky note and put it in the middle of a whiteboard. Find out why that is a problem by repeatedly asking 'So what?'. Find out the root causes by repeatedly asking 'Why (does this happen)?' Document your findings by writing more stickies and showing causal relations with arrows. Each sticky can have more than one reason and more than one consequence Vicious circles are usually good starting points for actions. If you can break their bad influence, you can gain a lot.
Visualize promise and ease of possible courses of actions to help pick Source: Tobias Baldauf
Reveal a previously drawn tree. Hand out round index cards and instruct participants to write down the actions they would like to take - one per card. When everyone's finished, collect the cards, shuffle and read them out one by one. Place each 'fruit' according to the participants' assessment:
Is it easy to do? Place it lower. Hard? More to the top.
Does it seem very beneficial? Place it more to the left. Value is dubious at best? To the right.
The straightforward choice is to pick the bottom left fruit as action items. If this is not consensus, you can either have a short discussion to agree on some actions or dot vote.
Let team members appreciate each other and end positively Source: Agile Retrospectives who took it from 'The Satir Model: Family Therapy and Beyond'
Start by giving a sincere appreciation of one of the participants. It can be anything they contributed: help to the team or you, a solved problem, ...Then invite others and wait for someone to work up the nerve. Close, when no one has talked for a minute.