Survivor

Terry and Sally messed up. Here's all they had to do:

Show the immunity idol to the whole group.
They should have told everyone that Terry will give the immunity idol to Sally no matter what. He of course has the hidden immunity idol himself. Therefore, it wouldn't matter who they voted for...either way someone other than Terry or Sally would have to go.
Rather than duke it out at tribal council, they should have just decided as a group who needed to go next. Everything would be out in the open.
Most likely they would have chose Aras to go next.
So all eight players go to tribal council and vote Aras out.
You know what?
The immunity idol is never shown because the threat of it coming out scares everyone away.

Bottom line: Sally and Terry are still in the game and Terry still has the immunity idol.

Why didn't they do this?