During After School's special tap performance of 'Let's Step Up', the stage partially collapsed. On April 29th, the girls had their comeback on KBS's 'Music Bank' with their new mini album title song, 'Shampoo'. To mark their comeback, they also gave a tap dance performance of 'Let's Step Up'. According to 'Music Bank', After School performed 'Shampoo' live but pre-recorded 'Let's Step Up.' Fans have been anticipating their 'Let's Step Up' performance for its special tap dance choreography. However, when they were tap dancing to their powerful choreography, part of the glass stage collapsed. An audience member who witnessed the incident stated, "After School's 'Let's Step Up' began with Kahi's solo, but I was surprised when a part of the stage collapsed." A picture that the witness shared shows the members showing surprised expressions when a part of the stage went down. After School members reportedly wore metal tap shoes on stage, and although the stage was made with strong glass, it collapsed due to Kahi's passionate and powerful solo. Fortunately, no one was hurt during the incident. After School's agency stated, "Members were surprised, but they are taking this as a sign for huge success. Kahi must have been too motivated [to perform]." http://www.youtube.com/watch?v=iSjVoYLxC5o Source: Nate