Sarah and Octopus

The Octopus sets up on the floor and the crowd closes in tight. So close that people two and three rows back can’t see anything but heads and shoulders. And that’s a shame, because if you don’t actually witness guitarist Mark Anthony Esquivel and bassist Ian McIntosh playing, you’re probably going to wrongly assume they’ve got cybernetic hands equipped with cutting-edge riff-processing units or, at the very least, a few extra fingers.

Case in point: proper opener “June 23rd,” book-ended by some improvised insanity, but most jaw-dropping for its bass line, an impossible-seeming mass of notes thumped out with inhuman speed. For many bands, this riff would be the highlight of a virtuosic jam session, a single, an irreplicable apex. Here it’s the damn hook, delivered repeatedly to structure drummer Mason Macias and Esquivel’s own mind-blowing in this musical three-ring circus act, while a girl rides a tiny bicycle through the crowd. Seriously.

Watching the band perform “Ajsu,” you can practically smell your synapses smoking like popped flashbulbs. Processing the beat on Macias’s drum parts probably requires a working knowledge of the quadratic formula, and Esquivel and McIntosh simultaneously finger-tap with both hands like they learned to rock the Mavis Beacon way. Occasionally they each seem to be playing extended solos from completely different songs. The effect is noisy, but felt less in the eardrum than the inner ear. That disorienting vertigo you feel is a symptom of Pastorius-Malmsteen syndrome — an always impressive whole that’s often less enjoyable than the sum of its individually incredible parts.

But on set-list centerpiece “Film School” the formula works. The athletic efforts of these three guys create the kind of bombastic beauty Broken Social Scene can only achieve with half the musicians in Canada.

Would-be closer “Wolves Dance Off Key” introduces entropy to the formula: Its dense, meticulously crafted opening devolves into a freeform freakout before it fizzles. It might’ve been a fitting conclusion, but audience-prompted encore “Choir,” a cool-off lap through which McIntosh sits Indian style on the floor, provides the most logical ending possible. “We don’t have any more songs,” Esquivel pants, sweat-soaked.