Taliesin was a Welsh poet of the A.D. 500s who inspired a well-known legend of Celticreferring to the Celts, early inhabitants of Britain whose culture survived in Ireland, Scotland, Wales, Cornwall, and Brittany mythology. It happened that a witch named Caridwen had a very ugly son. To make up for his looks, she decided to prepare a magic potion that would give him all the world's knowledge. However, the pot containing the potion had to boil for a year, so she asked Taliesin—then a poor farm boy named Gwion—to watch the pot for her.

One day the pot bubbled over, and a drop of the liquid splashed on Gwion's finger. When he licked his finger, he received one-third of the world's knowledge and the ability to change his form. He also realized that Caridwen was going to kill him when the potion was ready, so he ran away He assumed the shape of many animals but could not...