Your aim at each level is to have your tail as long as possible at the end of each round. You can simply swim over the tails. These tails are sometimes pink, sometimes green, and sometimes blue. You will see that your tail will turn into the color of the tail you collect, too! But more importantly, your tail will get a little bit longer with each tall you collect. This means you need to collect as many of them as you can before you complete the round. This being said, try not to hit the roller blades or the guillotines. They will harm you and shorten your tail, or worse, cause you to fail the level. You can rotate the mermaid with your cursor.