Chicken and Egg Story

Source 

Quite fancied a Monday morning teaser, so here's my attempt:
using System;
namespace ChickenEgg
{
public class Program
{
public static void Main(string[] args)
{
var chicken1 = new Chicken();
var egg = chicken1.Lay();
var childChicken = egg.Hatch();
var childChicken2 = egg.Hatch();
}
}
public interface IBird
{
Egg Lay();
}
public class Egg
{
private readonly Func<IBird> _createBird;
private bool _hatched;
public Egg(Func<IBird> createBird)
{
_createBird = createBird;
}
public IBird Hatch()
{
if (_hatched) throw new InvalidOperationException("Egg already hatched.");
_hatched = true;
return _createBird();
}
}
public class Chicken : IBird
{
public Egg Lay()
{
var egg = new Egg(() => new Chicken());
return egg;
}
}
}
Please don't just copy/paste this to your prospective employer without fully understanding what's going on. That would be a waste of everyone's time.