The Mars Volta's 2003 debut was a dense, experimental run-on sentence of science fiction and musical exploration.

But though it ultimately rewarded patience with stretches of unbuckled rock & roll genius, De-Loused in the Comatorium was also a maze-like and obtuse migraine dealer that made people frustrated and crazy.

For 2005's Frances the Mute, Omar Rodriguez-Lopez and Cedric Bixler-Zavala worked principally with their touring band, but "joining the band for selected moments" are strings, horns, electronic programming, pals Flea and John Frusciante, and the coqui frogs of Puerto Rico.

There are no song breaks, making the track listing more of an outline.

But Mute's printed lyrics are a helpful guide, a map of Mars that's meant to both direct and fascinate.

"She was a mink handjob in sarcophagus heels"; "Don't be afraid when all the worms come crawlin out of your head"; "they were scaling through an ice pick of abscess reckoning and when Miranda sang everyone turned away...." -- perhaps the only match for the cerebral weirdness and eventual beauty of Mars Volta's lyrics is their music itself.

The roar of Rodriguez-Lopez and Bixler-Zavala's post-hardcore past is fully locked away, replaced by an equally powerful flair for expressive percussion, intricate vocal harmonies, and extended solos for electric guitar (as on the initial part of "Cygnus...Vismund Cygnus").

Sure, there are moments on Mute that reach the grandiose heights of heavy music -- "L'Via l'Viaquez"'s ear-splitting changes will blow back your hair.

But the same song is sung half in Spanish, half in English, and its flashes of heaviness fall between stretches of Afro-Cuban rhythm.

Other portions of Frances the Mute are murky and distant, like field recordings from the ocean floor, while still others shift drastically between brittle acoustics and a stuttering, guitar-led volatility that threatens to crack open the earth.

Its constant shifts mean the record is claustrophobic and even dizzying; it demands perseverance.

But it's great when a blast of a trumpet cuts through a gloomy moment, and Bixler-Zavala's vocals are a thread to reality.

For example, while his lyrics for "Miranda That Ghost Just Isn't Holy Anymore" and "Widow" are mysterious poems, he sings them with a fervor that's immediately identifiable.

That passion is evident throughout Frances the Mute; it's the organic fever that was buried on Comatorium.