Which SM girl group songs have been most unique to you?

On a community forum, a netizen talked about the most experimental songs ever released by SM Entertainment girl groups. As a music label, SM Entertainment is known to have an A&R team that often mixes different beats contributed by songwriters around the world. Some have been produced through songwriters' camps and overseas collaborations. 

According to the netizens, some never-before-heard songs that have pushed boundaries are:

Girls' Generation - "I Got A Boy"

f(x) - "NU ABO"

Red Velvet - "Zimzalabim"

In the comments, fans of the label's experimental sounds also shared that Red Velvet's "RBB", f(x)'s "Red Light", and even Red Velvet's "One Of These Nights" are refreshing and unique.

Some comments include:

"I honestly think that 'I Got A Boy' was the most experimental....I was shocked when I first heard it"

"I love all these songs T___T especially NU ABO"

"For f(x) though, their concept is so experimental that everytime they came out with a song, it didn't feel weird or anything -- just well-suited to their image"

"LOL you might not like 'Zimzalabim' but hearing it at a concert will make you super pumped up"

"Even the lyrics are so experimental....they are like..new words"

"They are experimental but the addiction level is just as high"

What are some of your favorite experimental songs from SM Entertainment?