Poisoned chalice by TheRevSteve
Poisoned chalice, a photo by TheRevSteve on Flickr.

Today the church has been remembering John the Apostle and Evangelist (if you assume that they were the same person, of course).
Among the later legends which grew up around the man is one in which he was handed a chalice of poisoned wine. When he prayed, the poison left the wine in the form of a serpent.
This glass is a section of one of the windows in St. John’s College chapel, Cambridge.