i don’t know how fred and george would have figured out the exact words to use to work the map so i always imagine that they just happened to say those things and the map thought they were hilarious so it worked for them and they were like oh i guess those are the secret code words
"We have sworn, and not lightly. This oath we will keep. We are threatened with many evils, and treason not least; but one thing is not said: that we shall suffer from cowardice, from cravens or the fear of cravens. Therefore I say that we will go on, and this doom I add: the deeds that we shall do shall be the matter of song until the last days of Arda."
- Fëanor, Of the Flight of the Noldor - The Silmarillion
'And the doom of Fëanor was true-spoken also.' - The Annals of Aman, Morgoth’s Ring - HoMe