Inheritance problem

1

Can you take a look at this code?
Although noFoot has no feet he still has 20 fingers. What´s wrong here? Does he have 10 extra fingers coming out of his head?

function Extremities() {
	this.hands = 2;
	this.feet = 2;
}
Fingers.prototype = new Extremities();
function Fingers() {
	this.Fingers = this.hands * 5 + this.feet * 5;
}
twoFeet = new Fingers();
noFoot = new Fingers();
noFoot.feet=0
trace("twoFeet has " + twoFeet.Fingers + " fingers");
trace("noFoot has " + noFoot.feet + " feet");
trace("noFoot has " + noFoot.Fingers + " fingers");