My title is from the King James Version of the of the New Testament, Matthew 7:15-20, which relates Jesus' parable of the Tree and its Fruits. Here is the full version:

7:15 "Beware of false prophets, which come to you in sheep's clothing, but inwardly they are ravenous wolves."

16 Ye shall know them by their fruits. Do men gather grapes of thorns, or figs of thistles?