They rest their hooves on the hindquarters of the caribou in front of them, kind of like a chorus line forming across the tundra. Then they click their heels--tendons, actually--rhythmically and move in huge circles, periodically kicking their right hind legs out and grunting in unison. It's an awesome sight.
Anything else, yarb? I'm kind of running out of good caribou information.
Caribou have a tendon at the back of their leg that automatically snaps the leg back into walking position without the caribou having to expend any energy to do. You can hear it when they walk--even more impressive when you are listening to a large herd. The click isn't their hooves on the ground--it's the tendon snapping back into place.
"French explorers in Canada called the endless herds of caribou, the world's most efficient walkers, La Foule—'The Throng.' To see La Foule, as I had the previous summer ... is to be awestruck—there are so many caribou that an entire slop looks as if it is undulating. As they near, a chorus of grunting and clicking hooves accompanies the dramatic choreography of their movements."
—James Campbell, The Final Frontiersman (New York and London: Atria Books, 2004), 264–265