When you swing your penis up and down so it goes between your legs. When it goes between your legs it will reach between your ass cheeks and your ass cheeks will clench on your penis and you will pull it out rubbing along the taint
eventually leading to
ejaculation. Right before your penis gets clenched between your ass cheeks it makes a huge clap noise upon impact so you are essentially clapping your cheeks. This works best with
shit stains in your ass cheeks, they work as a lubricant.