The Raw and the Cooked

However, Finneces (Finegas) wanted to catch the "Salmon of Knowledge", called Fintan, and refused to teach anyone. Finneces had a change of attitude towards Finn, when after twenty years, Finneces finally caught the magic salmon on the bank of Boynne River.
The Salmon of Knowledge had eaten some nuts from the Tree of Knowledge. Anyone who caught and ate the salmon would be given wisdom.
Finneces thought that the youth was lucky. Finneces agreed to teach poetry to Finn, in return for the youth cooking the salmon for him. Finneces warned Finn that he must not eat any part of the salmon.
As Finn cooked the salmon, the youth tested to see if the salmon was ready by pressing his thumb to the fish side. The hot juice burned Finn's finger, which he placed his thumb in his mouth.
When Finn served fish to the druid, Finneces asked if the lad ate any part of the salmon. Finn replied no, but when he burnt his thumb he had placed it in his mouth. Finneces realised he was not destined to eat "Salmon of Knowledge", and told the young hero to eat the fish. Finneces saw no need to teach Finn and send him off.