Not sure if $.animate intend to support generic object.
The code below raise exception
"Uncaught TypeError: Cannot use 'in' operator to search for 'opacity' in undefined"
//===========================
var s = { opacity: 1 };
$(s).animate({opacity: 0}, 5000);

But it try to use $.css to set the opacity. So if I just change to other name
//===========================
var s = { opacity2: 1 };
$(s).animate({opacity2: 0}, 5000);
and it works.

I guess it might be resolvable If jquery can detect if it's the html object or not.
But not sure if $.animate intend to only support html object.