"Shock" is a song by the South Korean boy group Beast. It's the first single from their second EP "Shock of the New Era" which was released on March 1, 2010 along with the EP. The song introduced a new genre called Rocktronic, which is a combination of rock and electronic music.

A Japanese version was released on March 16, 2011 which serves as their debut single in Japan. It ranked #2 in the Oricon daily and weekly chart with 28,532 copies sold in the first week, beating the debut single of Big Bang's “My Heaven” at no. 3 in 2009.

In February 2010, Cube Entertainment announced that Beast will be returning into the music scene with a powerful chic black-toned concept, deviating from the image they portrayed from their debut single. "Shock" was originally set for release on March 2, 2010 together with the EP, but was moved back a day earlier because it was leaked on YouTube. Despite the leak, the song was able to enter the Top 10 Chart on different music portals.

"Shock (Japanese version)" is the official title of Beast's Japanese debut single. The song is sung in Japanese except for the rap portion which still remains in Korean. The single was released on March 16, 2011 and debuted at number 2 on the Oricon weekly singles chart.

The single was released in four different versions (Limited Edition A, B, C, and Regular Edition). The B-sides of each version vary from each other, all of which came from their different Korean EP's and are all sung in Korean. The accompanied songs are "Muni Dathimyeon" (문이 닫히면, lit. When The Door Closes), "Thanks To", "Let It Snow" and "Lights Go On Again (Full version)" which comes from their Korean digital album My Story, "Break Down" from Mastermind, and "Lightless" and "Niga Jeir Joha" (니가 제일 좋아, lit. I Like You the Best) from Lights Go On Again.

"Shock" is composed by Shin Sa-dong Tiger and Lee Sang-ho with the rap portion written by Beast member, Yong Jun Hyung. The song has a loop that sounds like you're listening to the guitar leap of heavy metal, and although it is brief, it harmonizes well with the heavy and fun rhythm of idol music. In addition with the strong beat, dynamic mood, and in reverse, with its sad sensitive lyrics, you can feel the lyrical emotions once you've listened to the song.

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Wikipedia