The bones in many freshwater fish are mainly used to support muscles. The weaker the fish meat, the denser the bones will be to provide stronger support.
Questioning:
Can we use the same rule to persuade someone?
Associating:
The muscle is like an opinion, the bone is like the argument to support it. Suppose the opinion itself is very evident and strong enough. In that case, we can use fewer arguments to support it, and the less obvious opinion may require more arguments to illustrate and support it.