using System;

using System.Collections.Generic;                   

public interface IAnimal

{

        string DoSound();

}

public class Dog : IAnimal

{

    public string DoSound()

    {

        return "Woof";  

    }

}

​

public class Cat : IAnimal

{

    public string DoSound()

    {

        return "Miaau"; 

    }

​

}

​

public class Program

{

    public static void Test(IAnimal animal)

    {

        Console.WriteLine("Animal");

    }

    public static void Test(Dog animal)

    {

        Console.WriteLine("Dog");

    }

    public static void Main()

    {

       var animals = new List<IAnimal>() { new Dog(), new Cat()};

        foreach(var thing in animals)

        {

            Test(thing);

            Test((dynamic) thing);

            Console.WriteLine(thing.DoSound());

        }

    }

}