This image from De Lamiis shows witches bringing down the rain. It looks like they are feeding the cauldron with a snake and a rooster.
Witches were feared for their ability to affect natural phenomena. For people whose lives were staked upon whether crops would fail or succeed, the elements were a fearsome unknown. A cold snap could kill the harvest, or too much or too little rain. If power to affect these elements was in the hands of malevolent neighbors, who were assisted by the devil, well, they were to be hated. And executed.
In The Witch's Trinity, townspeople whose village has been famine-struck look about themselves wildly to find who has kept the fields barren. And thus the witch hunt begins.
Image is from Witchcraft in Europe 1100-1700 by Alan C. Kors and Peter Edwards