Just avoid trying to explain to a newbie that what closures are and that you can pass functions around. That normaly === "mind blow"
The way you pass around functions in, say, PHP (or more accurately, the way PHP fakes it by using syntax sugar for eval) is a lot more confusing.
$addOne = function($a){ return $a + 1 };
$result = array_map($addOne, array(1,2,3)); // now [2,3,4]
// Reference to intval() function.
$result = array_map(intval, array('1','2','a'));