In the Westminster Confession of Faith 5.2, what does the Confession mean by "contingently"?

>Although in relation to the foreknowledge and decree of God, the first cause, all things come to pass immutably and infallibly, yet by the same providence he ordereth them to fall out, according to the nature of second causes, either necessarily, freely, or contingently. - Westminster Confession of Faith 5.2 Please give an example of a secondary cause that is contingent and tell on what it is contingent.