A dark, disturbing journey through the ugly underbelly of the human mind, "Aenima" is Tool's masterpiece.  Tool explores the brooding, seething psyche better than any band on the planet, and delivers its  message of existential dread with utter conviction.  The songs on  "Aenima" constantly shift, morph and transform themselves,  sometimes raging with fury, sometimes settling into relaxed interludes that  still boil with a dark menace underneath their calm surface.  Maynard James  Keenan's vocal work is the key to Tool's power, heard to maximum effect in  such songs as "Eulogy," "Stinkfist" and the title track.  No singer in rock  captures the ambivalence and terror of the human experience as well as  Keenan.  When he and his outstanding bandmates are at full speed, they're  untouchable.  "Aenima" will bore into your brain with all the  subtlety of a jackhammer.