: A "glass onion" is a layered object that is entirely transparent. Lennon used this to mock those trying to "peel back" his lyrics, suggesting there was nothing hidden beneath the surface.
: The song features a driving rhythm track, Paul McCartney’s distinctive recorder part during the "Fool on the Hill" reference, and an eerie string arrangement by George Martin. Glass Onion (Remastered 2009)
List other found in the lyrics (like "the Cast Iron Shore"). : A "glass onion" is a layered object