$(document).ready(function() {

  $("#fast_fact_container").hover(function() { //On hover...

    var thumbOver = $(this).find("img").attr("src"); //Get image url and assign it to 'thumbOver'

    //Set a background image(thumbOver) on the <a> tag - Set position to bottom
    $(this).find("a.thumb").css({'background' : 'url(' + thumbOver + ') no-repeat center bottom'});

    //Animate the image to 0 opacity (fade it out)
    $(this).find("span").stop().fadeTo('normal', 0 , function() {
      $(this).hide() //Hide the image after fade
    });
  } , function() { //on hover out...
    //Fade the image to full opacity 
    $(this).find("span").stop().fadeTo('normal', 1).show();
  });

});