Congratulations, Charli XCX and Halsey: You've officially discovered the surefire way to make an entire festival crowd lose their minds in seven words or less, and those seven words are "YOOOO I'LL TELL YOU WHAT I WANT!"
The singers — who are hitting the road together in September on Halsey's Hopeless Fountain Kingdom World Tour — joined forces for a surprise Spice Girls cover during Charli's Lollapalooza set on August 6. Ever the sneaky one, Halsey dropped a pretty sizable hint about the duet via Instagram shortly before she joined Charli and the zig-a-zig-ahs kicked in.
Two seconds into the first verse, those gathered to see Charli were bouncing in one giant group, and they clearly had just as much fun as Charli and Halsey did.
Watch their impromptu performance — otherwise known as the Stuff Millennial Music Festival Dreams Are Made Of — in full below.