function animalNavMenu()
{
   $(".animalImg").hover( function() {
       var hoverImg = HoverImgOf($(this).attr("src"));
       $(this).attr("src", hoverImg);
     }, function() {
       var normalImg = NormalImgOf($(this).attr("src"));
       $(this).attr("src", normalImg);
     }
   );
   
   $(".animalImg2").hover( function() {
       var hoverImg = HoverImgOf($(this).attr("src"));
       $(this).attr("src", hoverImg);
     }, function() {
       var normalImg = NormalImgOf($(this).attr("src"));
       $(this).attr("src", normalImg);
     }
   );    
    
}

//eg. submit.png and submit_hover.png
function HoverImgOf(filename)
{
   var re = new RegExp("(.+)\\.(gif|png|jpg)", "g");
   return filename.replace(re, "$1_hover.$2");
}
//eg. submit.png and submit_hover.png
function NormalImgOf(filename)
{
   var re = new RegExp("(.+)_hover\\.(gif|png|jpg)", "g");
   return filename.replace(re, "$1.$2");
}