After a brief discussion, they proposed a good plan. They tried to make the mussel the scapegoat for the recent disappearance of the majestic beings. If they could convince others, they had more than enough reasons to kill it. Hence, they carefully planned each step and then set the plan in motion.
For instance, once the mussel was dead, one of them would offer one of his least favorable majestic beings and kill it with the mussel's shells. By doing so, they could easily fabricate the charge against the mussel. When the structure of their plan was finally well made, they started to surround the mussel.