Twitter Bootstrap Class Animation

HTML

<link rel="stylesheet" href="//netdna.bootstrapcdn.com/twitter-bootstrap/2.2.1/css/bootstrap-combined.min.css">
<div class="container-fluid">
    <div class= "row-fluid">
        <div class="span6">
            <h1>CSS</h1>
            <img src="http://placehold.it/140x140" class="img-circle css">
        </div>
        <div class="span6">
            <h1>jQuery</h1>
            <img src="http://placehold.it/140x140" class="img-circle js">
        </div>
    </div>
</div>

CSS

img {
    cursor:pointer;
}
img.css {
    -webkit-transition:border-radius 0.8s linear;
    -moz-transition:border-radius 0.8s linear;  
    -o-transition:border-radius 0.8s linear;      
    transition:border-radius 0.8s linear;  
}
    img.css:hover {  
        border-radius: 6px;
    }

JavaScript

$(".js").hover(function() {
    $(this).animate({
        "border-radius": "6px"
    });
}, function() {
    $(this).animate({
        "border-radius": "500px"
    });
});