The dancers are chanting "Odoru aho ni miru aho; onaji aho nara odoranya son son!" - "It’s a fool who dances and a fool who watches; if both are fools, you might as well dance!", so the dance was nicknamed "the dance of fools".
EXIF info:
Nikon D90
Lens: VR 18-55mm F/3.5-5.6G
Focal Length: 20mm
Aperture: F/5.6
Shutter Speed: 1/60s
ISO Sensitivity: ISO 320