The Hidden Lore
So the party finds this incantation when they’re looking for something else. Preferably under circumstances where they know that the incantation is not a forgery, a hoax, or anything else. Hand it to them, absolutely casually.
HYOL M’DHAMDL H’RADA FHRAM!
IA! IA! OH!
ABNON-ZAT FHRAM HEHT-A-DA KOO!
IA! IA! OH!
WZTAH MEH-MU HY’R
AMDA MEH-MU T’TR
HY’R AMEH! T’R AMU!
AZO-THOTH AMEH-MU:HYOL M’DHAMDL H’RADA FHRAM!
IA! IA! OH!
If anybody reads it aloud, stop them after the first word, take that player to another room, tell him You feel an irresistible urge to sing it to the tune of “Old MacDonald,” and then you both go back to the other room and rewind the game to just before the player started to read the text aloud. Then see what happens.
…That’s it.