“O horror, horror, horror!”
— William Shakespeare, Macbeth (1606)
Context
Macduff has just discovered the murdered body of King Duncan and is the first to put words to it. The exclamation precedes any coherent account of what he has seen, as if the act of repetition is the only utterance available before description becomes possible.
How the repetition works
The triple "horror" registers as pre-linguistic shock — Macduff's mind has not yet caught up with what his eyes have witnessed. Each repetition buys him another moment before he must form a sentence. The line is a study in how language can fail and survive at once.