For every action, there is an equal and opposite reaction. Even in the bizarro world of The Mars Volta -- though, like everything they do, it doesn't happen in a hurry.

On their first two CDs, the uncompromisingly adventurous outfit helmed by singer Cedric Bixler-Zavala and guitarist Omar Rodriguez-Lopez delivered a massive freakout of unhinged prog-metal that melted your brain with its relentless intensity and fever-dream vibe. For Amputechture, their fourth disc in as many years, the At the Drive-In refugees lower the dosage a tad.

On this 76-minute trip, the grooves are a little slower and straighter, the melodies are a little more prominent, the songs are a bit quieter and spacier (in every sense of the word) -- and most of the time you can make out what Cedric is howling.

Of course, you still have no idea what he's talking about when he sings stuff like, "Glossolalia coats my skin / Glycerin and turbulence." And between the band's short-attention-span antics and an average song length of nine minutes, there's plenty of shape-shifting sonic weirdness to go around, from the free jazz skronking of Vicarious Atonement to the backwards-tape manipulations of Tetragrammaton to the mutant funk-rock and jazz-fusion of Viscera Eyes to the piercing licks of Red Hot Chili Peppers guitarist John Frusciante.

Bottom line: Even in a slightly mellower mood, The Mars Volta are far and away the freakiest dudes in rock.

Thankfully, we don't suspect that to change in a hurry either.

Track Listing:

1. Vicarious Atonement
2. Tetragrammaton
3. Vermicide
4. Meccamputechture
5. Asilos Magdalena
6. Viscera Eyes
7. Day Of The Baphomets
8. El Ciervo Vulnerado