Difference between Crumb and So-and-so

Crumb

Part of speech: verb

Definition: To cover with crumbs.

Part of speech: noun

Definition: A small piece of baked food (such as cake, biscuit or bread). A bit, small amount. The soft internal portion of bread, surrounded by crust. A mixture of sugar, cocoa and milk, used to make industrial chocolate A nobody, worthless person. A body louse.

So-and-so

Part of speech: noun

Definition: A placeholder name, used when a name is not known; a generic name.Anything generic.A name used to take the place of an epithet.