the meaning or sense of a
situation, remark, joke, etc., is finally made evident or grasped after a
period of delayed noncomprehension or misunderstanding. This
phrase is probably a
reference to
coin-operated machines which require a
coin be
dropped into a necessary
position before they begin to operate.
(colloquial) the meaning of a remark, joke, etc., is finally understood; the desired
effect is gained after a
period of misunderstanding. From the
use of machines operated by
coins. The machines will not
work until the
coin has
dropped into the necessary
position.