Name your fiddle

Description

HTML

<div class="tweet-stream"></div>

CSS

.tweet-stream
{
    border: 2px solid black;
}
.t-header
{
    border: 1px solid silver;
}

JavaScript

var side = 'left';
cnt = 0;
setInterval(function () {
    $(".tweet-stream").prepend("<div class='tweet t" + side + "></div><div class='t-header'>tweet-" + cnt + "</div>");
    if (cnt % 2 == 0) {
        side = 'right';
    } else {
        side = 'left';
    }
    if (cnt >= 5) {
        $("div.tweet:last").remove();
    }
    cnt++;
}, 3000);