about virtual and override confuse

gistfile1.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Obj5
{
    class Program
    {
        static void Main(string[] args)
        {
            Car c = new Car();
            c.Brand = "BMW";
            c.Name = "Z4";
            // 轉型之後為何拿的到 Brand
            // Readme: http://msdn.microsoft.com/zh-tw/library/ms173153%28v=vs.80%29.aspx
            ((Vehicle)c).Run();
            Console.ReadKey();
        }
    }

    public class Vehicle
    {
        private string name;
        public string Name { get; set; }
        public virtual void Run()
        {
            Console.WriteLine(this.Name + " Go!");
        }
    }

    public class Car : Vehicle
    {
        private string brand;
        public string Brand { get; set; }
        public override void Run()
        {
            Console.WriteLine(this.Brand + "Go Go ");
        }

    }
}