Fintan Finegas: Biting the Thumb Swelling with Wisdom (親指かむかむ智慧もりもり, Oyayubi Kamukamu Chie Morimori?) is the anecdote of the wisdom granted to Fionn mac Cumhaill from the oil of the Salmon of Knowledge becoming a Noble Phantasm. Because of this salmon's fat that remained attached to one of Fionn's thumb, it is said that licking it quickly will grant great wisdom. This Noble Phantasm is the origin of the Uisce Beatha Noble Phantasm as the latter depends on this very anecdote.
Perhaps there seems to be another true name for this Noble Phantasm. By the way, the fat of salmon contains a lot of DHA which increases concentration.