- Hermione: "This is Felix Felicis, I suppose? You haven't got another little bottle of -- I don't know--"
- Ron: "Essence of Insanity?"
- Harry: "Trust me, I know what I'm doing... or at least Felix does."
- — Ron and Hermione become suspicious after Harry takes Felix Felicis and says he's going to see Hagrid[src]
Essence of Insanity is a potion which presumably causes irrational behaviour, possibly inflicting the condition of insanity. Ron Weasley wondered if Harry Potter had consumed this instead of Felix Felicis on 21 April, 1997.
Behind the scenes
- It is unknown if Ron was referring to an actual potion, or was merely speaking metaphorically.
- Harry Potter and the Half-Blood Prince (First mentioned)