I always get the urge to think deep thoughts at Tool shows — thoughts about evolution and decay and what it means to be human. Unfortunately, few ever come to me. Instead, I offer a diary of useless theories developed over the course of a couple of hours last Friday at the FleetCenter while watching the only prog-metal band who matter.

Tool are big on video screens. Before they go on, the screens show a pattern of eyes arranged in a circle and using colors usually reserved for dorm-room blacklight posters. Eee-yewww. (Useless theory #1: Tool are actually the Grateful Dead.)

Great way to open a show: play your all-time greatest hit first. For "Sober," Maynard Keenan appears in his usual stance — awkwardly hunched, like Max Schreck in Nosferatu — wearing jacket and pants instead of his usual kabuki-crossdresser garb. The rest of the band look like LA session dudes, with professional hair just like that on the guys in Megadeth or Dream Theater. (Useless theory #2: Tool are actually Dream Theater.)

During "The Grudge," video screens show a human head with an extra eye in the forehead using CGI animation that looks a few years out of date. Maynard keeps time with a mule-kick leg stomp, just like Les Claypool. (Useless theory #3: Tool are actually Primus.) The animation is less mesmerizing than Danny Carey’s kit, which includes several thousand drums, a couple of computers, a gong, and a coffeemaker. Carey is also wearing Lakers warm-up gear, which is wicked uncool at the Gahhhden, dood. Correction: Maynard is not entirely free of weird make-up. He’s got a mohawk that, thanks to a racing stripe of black greasepaint, continues straight through his face to his chin. (Useless theory #4: Maynard’s a twerp.)

Just before "Stinkfist," Maynard rattles off an impressive list of Boston suburbs — either he bought a map or the rumors about his having lived in Somerville a few years back are true. They debut a cool lighting device: fake Tesla coils above the stage. (Useless theory #5: Tool are actually Tesla.)

After seeing Tool play "46 + 2," I still have no insights into the mystical underpinnings of homo sapiens’s chromosomal structure — but I sure remember why I hate drum solos and interpretive modern dance. (Useless theory #6: Maynard is actually Mark Morris.) Before "Schism," Maynard launches into a soliloquy about the need for world peace. (Useless theory #7: Maynard is actually Bono.) During "Schism," stagehands backstage wrestle with what look like two immense bunches of inflatable grapes. What the hell’s that all about?

Maynard strips down to Speedos for "Parabol"/"Parabola." The giant grapes (of wrath?) hover in midair behind the stage on twin jets of pressurized air. Sudden realization: floating grapes are wicked cool. The Globe’s Steve Morse is utterly baffled. Turning to the fan he’s been bugging for song titles all night, he wonders aloud, "How do they keep those balloons up? You think it’s strings?" Wish they could rig a string for Maynard’s undies: halfway through "Parabola," I can see his butt crack. Double eee-yewww. (Useless theory #8: giant grapes are Maynard’s man-berries.)

After a brief intermission, the backdrop behind the band changes — another freaky circular eyeball pattern. (Useless theory #9: if you look at the backdrop long enough, you’ll see a three-dimensional image of Adrian Belew’s cock ring.) Video screens show shadowy bodies floating in water while the band play "Disposition," a shadowy-bodies-floating-in-water kind of number. Topic for discussion: didn’t Nine Inch Nails do better shadowy-bodies-floating-in-water songs on The Fragile? Anatomical illustrations drop from the rafters for "Reflection," some of them showing the locations of chakras or something. Note to self: remember to ask Madonna about it the next time she’s in town. Also, a big weird silver star-of-David-like thing descends from ceiling. Did anyone know Tool were Jewish?