[theholycow]

Not a sample because they didn't sample it from PF's recording. Not a cover because they're only using part of it in part of their song. Not sure what you'd call it.

Actually, the portion they used doesn't seem to be exactly covered either, more that it just sounds a lot like a PF song.

For a similar example, check this shit:
Shooter Jennings - Busted In Baylor County; at 2:08 you hear a couple seconds of a riff from Black Sabbath's "Sweet Leaf"

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In live versions he plays 10-30 seconds of the song and sings "All right now!" as Ozzy did.

Original:

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In this case I'd call it a shout out to Black Sabbath, but what DMB did was more...not sure what to call that.