php的静态方法调用有关问题，求大牛解答

class Cat {
}
class Hypnotic_Cat extends Cat {
// Constructor
	function Hypnotic_Cat( ) {
	}
// This function must be called statically
	public static function hypnotize( ) {
		echo ("The cat was hypnotized.");
		//return;
	}
}
// Hypnotize all cats
//Hypnotic_Cat::hypnotize( );
$hypnotic_cat = new Hypnotic_Cat( );
// Does nothing
$hypnotic_cat->hypnotize( );
?>