You can't let the fish you dropped get away! You take a breath and dive underwater, your whiskers telling you more then you can even understand. The fish has obviously hidden itself well, but you can tell others are around. You pick one, and begin to chase after it...but this is too fast, and tuns faster then you can!
You have no hope of catching it, but you suddenly do...in fact, swimming is becoming nothing more then a game, turns and twists and everything are as easy as if you'd been born underwater. And you don't really feel out of breath, though you know you've been down for a long time.
You resurface, not to breathe, but to eat. Without thinking you flip on your back and...suddenly notice the tail you've grown. It must be a full five feet long! No wonder you could swim so well.