Alas! I have little time today. So I'll post on something brief: interjections! Anything can be an interjection if you punctuate it correctly. Airplane! See how that works?
And how lovely to discover that holla was a word in the Victorian lexicon! Though it had a completely different meaning, which puts it in company with other migratory words like gay and nice. Oh, language, with its twists and turns.