The Salmon of Knowledge

The salmon of knowledge was an ordinary fish until it consumed the nine hazel nuts that fell into the Well of Wisdom from nine hazel trees that surrounded the well. In so doing the salmon gained all the knowledge in the world.

Knowing that eating the flesh of the salmon would grant him all knowledge, the legendary Irish poet Finegas spent seven years seeking the fish.

While struggling to net the wily fish Finegas accidentally looked into it's eyes and immediately fell into a deep sleep.

Finegas' apprentice, Fionn mac Cumhaill, saw him asleep and rushed to wake him before the salmon could escape.
Finegas blindfolded himself so that he would not be affected by the salmon's spell and cast his net again and again. Eventually after a great struggle he succeeded and the Salmon of Knowledge was caught.

Tired from his exertions Finegas charged Fionn with cooking the fish and warned him not to eat it. While cooking the fish Fionn's thumb was spattered with hot fat and he immediately sucked on it to ease the pain.

When he brought the cooked meal to his master, the poet saw a fire in the boy's eyes that had not been there before. Fionn denied that he had eaten the fish, but when pressed, he admitted his accidental taste.

Thereafter, whenever Fionn put his thumb in his mouth, he could access the wisdom and knowledge gained from the salmon.
This gift that allowed Fionn to become the leader of the Fianna, the famed heroes of Irish myth.