toggleClass question

toggleClass question

Still new to javascript and jquery, and have a tone of questions. Some I am getting answered by documentation....I tried the toggleClass function on an image and obviously it works. but if the class is toggled why does the below function work always? It seemed to me it should work once then the class is changed to markunread and it should not work again...

$(".markread").click(function() {
$(this).toggleClass("markunread");
});

Thank you very much
maddogandnoriko