Actionscript:

var xp:Number = 0;

var yp:Number = 0;

var t:Number = 0;

var a:Number = 200;

x = stage.stageWidth / 2;

y = stage.stageHeight / 2;


graphics.lineStyle(0,0x000000);

addEventListener(Event.ENTER_FRAME, onRun);

function onRun(evt:Event):void {

xp = a * Math.cos(t)  (a * Math.pow(Math.sin(t),2))/Math.sqrt(2);

yp = a * Math.cos(t) * Math.sin(t);

if (t == 0){

graphics.moveTo(xp, yp);

}else{

graphics.lineTo(xp, yp);

}

t += 0.05;

}
While surfing mathworld I stumbled upon the equation for something called the Fish Curve. This snippet will draw something like this: