The legend of St. Guinefort dates to the Thirteenth century, when a cult grew up around Lyon, France dedicated to the worship of this holy saint.  As the Legend goes, Guinefort was a favourite of his master, we'll call him Bob, second only, in fact, to Bob's young son.  One day, Bob went out for a day of hunting leaving his son in the care of the favoured Guinefort.  When hereturned he found his son's room torn to pieces and Guinefort sitting in the middle of the floor covered in blood.  Unable to find his son, Bob struck Guinefort dead in a single blow and threw the body down a well.  Returning to his son's room to grieve, Bob heard a cry, turning over the child's bed he found his son safe and sound next to the body of a huge python.  In an instant the master realized what had happened, Guinefort had bloodied himself by killing the snake and saving the child's life.  Full of remorse, Bob converted the well in to a shrine and the people of the surrounding area began to worship Guinefort as a saint and protector of small children.  It may be important to note at this stage that Guinefort was a greyhound.  Eventually the papacy heard of the holy dog and sent a legate around to tell the people to knock it off with the animal worship.

For more about St. Guinefort, please visit the Internet Medieval Sourcebook:
Stephen de Bourbon (d. 1262): De Supersticione: On St. Guinefort
http://www.fordham.edu/halsall/source/guinefort.html