The problem with mixed metaphors is not
primarily that two or more diff'rent
comparisons are being mixed, but that
the two comparisons are expected,
and so, dead. The power inherent in
a metaphor is this: the surprise found
when a song takes up its mat and walks out
of the house and makes its bed in your heart.
A mixed metaphor is better than one
that is dead - at least the surprise shocks you
out of expectancy and into thought:
the very thing that which is dead could not.