"Learn to swim, learn to swim, learn to swim, learn to swim…"

On Oct. 1, 1996 (Sept. 17 on vinyl), Tool unleashed one of their career-defining albums, Ænima, an essential release for the golden age of '90s alternative rock. Before Ænima went on to sell more than 3 million copies in the U.S. alone, Tool were known primarily has a hard rock band with a penchant for heavy grooves, expressing anger and exploring dark subject matter. With the introduction of Ænima, however, prior psychedelic nuance became a full-on trip while songs became longer and increasingly dense.

Though there may have been a shift in focus, Tool's dry yet flippant scatological humor remained constant. The album title itself refers to psychologist Carl Jung's own term for the soul, "anima." Throw in the alternate name for an anal douche and you wind up with the heavily digested Ænima. "It's about change, cleaning out the house to refurbish or redecorate and start over," frontman Maynard James Keenan told Carrie Borzillo in a 1996 interview.

That change may not have been instantly noticeable once fans popped Ænima into their CD players, as the opening track, "Stinkfist," seemingly picks up where Tool's previous release, Undertow, left off three years previous. Ænima really begins to take its own shape once the massively distorted "Eulogy" and soul stirring "H." creep into the listener's ears. The two tracks act as heavy breaths of sonic meditation, offering a highly sophisticated sense of calm which branches off from Tool's trademark intensity like a fraternal twin.

Drummer Danny Carey specifically grabbed the near-religious Tool fans with his performance on the first three Ænima tracks, expanding his comprehensive kit even further by using electronic pads, most notably the Simmons SDX. "The zone intelligence on those pads is amazing," Carey told Matt Peiken in 1997. "With just a multitude of options and parameters, and there's no limit with whatever I want to do in terms of dynamics or blending sounds." Carey's experimentation offered seemingly endless possibilities for the ever-opening third eye of Tool and raised his own status as a modern day master of percussion.

Ænima also marked the introduction of bassist Justin Chancellor, who was welcomed into the fold after Paul D'Amour's leave in 1995. Chancellor took to his instrument as a pure bassist, embracing the smooth, swirling elements of the bass compared to D'Amour's more abrasive, guitar-like attack. Chancellor's new influence is apparent on "Forty Six & 2," which the bassist had a heavy hand in composing. Twenty-one years after its release, "Forty Six & 2" is still one of Tool's most discussed songs among fans, with the most popular theory being the subject of human evolution. Current human DNA contains 44 autosomes and 2 sex chromosomes, and touching on Carl Jung once again, "Forty Six & 2" chronicles the next step in evolution to 46 autosomes.

After branching out to subjects most bands would never dare touch, Tool brought it back to anger on "Hooker with a Penis." The song's story tells itself while Maynard barks the words, "I met a boy wearing Vans, 501s, and a Dope Beastie tee, nipple rings, and new tattoos that claimed that he was OGT (Original Gangsta Tool) back in '92 from the first EP." After being accused of selling out by the gentleman, Maynard replies in tongue-in-cheek fashion, "I sold out long before you ever heard my name."

After two interludes and the traumatic "Jimmy," Ænima dives into the 10-minute opus "Pushit," one of many tracks where guitarist Adam Jones really shines. Jones' guitar buzzes through a hypnotic and unconventional (even for Tool) riff in 3/4 before spending much of "Pushit" brilliantly controlling feedback through his monstrous pedal board. The wormhole weaving of "Pushit" is almost a giant crescendo meant to bring Keenan's cry of "I must persuade you another way" to its utmost peak. It's one of the moments Tool fans await an entire show, and once the band's instrumental section drops out, Keenan's soaring high note imparts a feeling of weightlessness only to spike the listener back to earth with, "Remember I'll always love you, as I claw your f---ing throat away."

The pseudo-title track of Ænima, "Ænema," tips a hat toward legendary comedian Bill Hicks, who had passed away from pancreatic cancer two years earlier. Hicks and the collective consciousness of Tool seemed to be kindred spirits, and the brainstorming of both minds resulted in "Ænema," a good-riddance letter written to the city of Los Angeles. Once again, Tool's precise dissection of the very nature of anger remerges as Maynard Keenan unleashes a flurry of f-bombs and wills L.A. into the Pacific Ocean, "Cause I'm praying for rain / And I'm praying for tidal waves / I wanna see the ground give way / I wanna watch it all go down."

Ænima finishes up with the near 14-minute "Third Eye," a somewhat unheralded opus of Tool's career. Also inspired by a Bill Hicks bit, "Third Eye" speaks to a lost means of perception in today's culture. "You literally have a third eye in your head," Keenan explained in a 1996 interview. "It's your pineal gland and it is an eye. It focuses light. People talk about dolphins and whales being more evolved, because they have a better breathing element. If you do meditation, you understand the idea of the Prana, breathing in light through the pineal gland. In mythology, there's talk about how people used to breathe that way, but over time, they began to breathe more through the mouth. That's the connection that we've forgotten … Your consciousness is like a radio frequency. If you turn the dial, all those radio stations are there simultaneously. You can dial in to hear what station you want to hear. Consciousness is the same way. Through meditation, you can alter that, you can come upon an alternate reality. Drugs is a shortcut to that. The trick is to really understand the medium you used to get there."

To this day, no band sounds quite like Tool. Furthermore, no Tool album sounds quite like Ænima. It's an enigma never to be replicated, the blueprint pieced together by the hand of nature and hidden away after the fact. Brilliant from beginning to end, Tool's Ænima remains just as relevant, fresh and celebrated as it was in 1996.