The reason is that a German netizen made an anime MAD, and the soundtrack was Caramelldansen, the electronic music of Swedish music group Caramell. Inspired by this MAD, a Japanese otaku intercepted the picture of the character's hands swinging and twisting his waist in the opening MV of POPOTAN, and played it in a loop with Caramelldansen. Another netizen even accelerated Caramelldansen's speed to 1.20% (later this song was called Caramelldansen Speedy Cakerremix) to match the "waist-twisting" movements of various anime characters, thus forming the popular "waist-twisting dance" on the Internet.