"swine to jump over a cliff"

The reference is to the bible story of the Gadarene swine in chapter 5 of the gospel of Mark. Jesus exorcised demons from a possessed man.  The demons then entered a herd of pigs, which rushed off a cliff in a frenzy.

And forthwith Jesus gave them leave. And the unclean spirits went out, and entered into the swine: and the herd ran violently down a steep place into the sea, (they were about two thousand;) and were choked in the sea.  (St James Bible).