Discover the leader
Have the group sit in a circle. Ask for a volunteer and have her leave the room. In the room tell the group that they have to do different things like clapping, snapping your fingers, tapping your feet, etc. But these actions have to be initiated by somebody in the group and after a few moments of everybody catching on and doing the same actions, somebody else can take on to change the action. Then the rest of the group catches on and continues with the new action.
For instance if somebody in the group starts to clap, others should clap as well. After a minute or two of clapping, somebody else can start to snap their fingers. Slowly the group starts to catch on and starts to snap their fingers for a minute or two. This way the group does various such actions. Tell the group that their aim is to make it difficult for the volunteer to guess the leader.
While the group plays this game, the volunteer is called in and asked to guess at the leader. It is really interesting to watch the volunteer trying to guess the leader. If the group has practiced well and focusses on collaboration rather than competition, it will be difficult for the volunteer to catch on and identify the leader - the person or persons who are initiating the actions.
The debrief of the game is to talk about what aided the collaboration in the group and what hindered it. You'll be able to help the group come to the conclusion that communication is a means for collaboaration rather than competition.