The posterior of any individual is not capable of intelligence. You are aware of this fact and yet continue to use that term. [ There are aspects of humanity Spock does not comprehend and is unsure if she will ever comprehend.

She teases Jim only because she is comfortable enough with him to do so, knows he understands the uniqueness of Vulcan humor. ]

It is impossible for an idiom to apply to everything, as everything encompasses even that which we do not yet know. [ As far as her arguments go, it is not a strong one. But they have relaxed enough that she can let the argument rest. ]