class Test
{
	protected $x = 2;
	
	public static function first_method()
	{
		return $this->x;
	}
	
	public static function second_method()
	{
		return 'cant use $this in static methods';
	}
	
	private static function third_method()
	{
		return 'you cant call me na na na na na';
	}
}

Test::first_method(); // Fatal error: Using $this when not in object context
Test::second_method(); // the right call
Test::third_method(); // Fatal error: Call to private method Test::third_method() from context ''