When you study the original short film and the opening of 'Oh Hae Young Again,' you can't help but notice that the scenes are very much alike. 

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tvN admitted that they did refer to 'The Sound of COS' and relayed their intent to contact the original makers to consult them about the copyrights as well as to discuss how to appropriately credit them.  

A tvN rep stated, "There are parts in 'Oh Hae Young Again's opening title which is similar to the work that it references, and on the seventh episode which will broadcast this May 23, we decided to air the opening title after deleting those scenes. We want to apologize for not being more careful in the making of the opening title video."

You can view the opening title and the original art film for yourself in the clips provided.