[Decode]

Например, так:

<style>
    .block {
        width: 200px;
        height: 100px;
        border: 2px solid #ccc;

    }

    .active {
        background: #ccc;
    }
</style>
<div class="block">
    <p>Bla-bla</p>
</div>

<script src="http://code.jquery.com/jquery-latest.min.js"></script>
<script>
    var txt = $('.block').children('p').text();

    $('.block').on('click', function(event) {

        $(this).toggleClass('active');
        $(this).children('p').text( $(this).children('p').text() == txt ? 'Tra-ta-ta' : txt);
    });
</script>