Seven years passed between the release of 'Bone Machine' and 'Mule Variations'. During that time Tom Waits eschewed cutting another conventional (the term used loosely here) song collection, occupying his time with acting projects, a soundtrack ('Night on Earth'), a stage project ('The Black Rider'), and sundry smaller diversions. What's surprising about 'Mule Variations' is how little he's strayed from the old bone yard through the years. As with his grammy-winning 1992 outing, Waits intersperses the tough and the tender, mixing exercises in creative noisemaking with tunes that fall on just the right side of maudlin. As with 'Bone Machine''s 'The Ocean Doesn't Want Me', 'What's He Building?' is an experiment in word jazz that owes a debt to its creator, Ken Nordine. Waits has again assembled a crew of attuned sidemen (including Primus and steadfast backers Ralph Carney, Larry Taylor, and Joe Gore). And, as always, Waits and his wife - co-songwriter co-producer Kathleen Brennan exhibit an uncanny ear for the arcane.