We've already seen how 'Dazed and Confused' and 'Houses of the Holy' displace one beat (though in opposite directions), how 'When the Levee Breaks' displaces one measure, and how 'Stairway to Heaven' displaces by two beats and by an entire phrase.
Next and last in this series is a song that displaces half a beat: 'Black Dog', the initial track of Led Zeppelin IV (1971).
In this case, a seven-note pattern lasting nine eighth notes...
...is repeated over common time measures, yielding rhythmic displacement of a single eighth note (half a beat) per iteration.
Lesser musicians might have repeated these musical ideas more or less the same each time. But Zeppelin, ever attentive to detail, found ways to subtly alter their music in a way simultaneously familiar yet different through rhythmic displacement. And that, I suspect, is one trait (of many) that separates the good bands from the great bands.
Aaron Krerowicz, pop music scholar
An informal but highly analytic study of the music of Led Zeppelin.