Interface vs Base class

public abstract class Mammal

public class Dog : Mammal
public class Cat : Mammal

public class Giraffe : Mammal
public class Rhinoceros : Mammal
public class Hippopotamus : Mammal

public interface IPettable
{
    IList<Trick> Tricks{get; set;}
    void Bathe();
    void Train(Trick t);
}

public class Dog : Mammal, IPettable
public class Cat : Mammal, IPettable

public class Pet
{
    void Bathe();
    void Train(Trick t);
}

public class Dog
{
    private Pet pet;

    public void Bathe() { pet.Bathe(); }
    public void Train(Trick t) { pet.Train(t); }
}

public class Cat
{
    private Pet pet;

    public void Bathe() { pet.Bathe(); }
    public void Train(Trick t) { pet.Train(t); }
}