function over(img_name) {
  bunni = document[img_name].src;
  document[img_name].src = bunni.substring(0,bunni.length-4) + "_over" +  bunni.substring(bunni.length-4,bunni.length);
}

function out(img_name) {
  bunni = document[img_name].src;
  document[img_name].src = bunni.substring(0,bunni.length-9) + bunni.substring(bunni.length-4,bunni.length);
}