C++ virtual functions

[sonulohani]

Sir,
I have a query about this vitual function. Look at this example:-

using namespace std;
 
#include <iostream>
class Animal {
    public:
         void eat() {                   //I have removed the virtual keyword here.
                cout << "I eat like a generic animal.\n";
        }
        // polymorphic deletes require a virtual base destructor
        //virtual ~Animal() {
        //}
        };
        class Wolf : public Animal {
            public:
                void eat() {
                    cout << "I eat like a wolf!\n";
            }
        };
        class Fish : public Animal {
            public:
                void eat() {
                    cout << "I eat like a fish!\n";
            }
        };
        class GoldFish : public Fish {
            public:
                void eat() {
            cout << "I eat like a goldfish!\n";
            }
     };
int main() {
    Animal animal;
    Wolf wolf;
    Fish fish;
    GoldFish goldfish;
    animal.eat();
    wolf.eat();
    fish.eat();
    goldfish.eat();
    return 0;
}

using namespace std;

#include <iostream>
class Animal {
    public:
         void eat() {                   //I have removed the virtual keyword here.
                cout << "I eat like a generic animal.\n";
        }
        // polymorphic deletes require a virtual base destructor
        //virtual ~Animal() {
        //}
        };
        class Wolf : public Animal {
            public:
                void eat() {
                    cout << "I eat like a wolf!\n";
            }
        };
        class Fish : public Animal {
            public:
                void eat() {
                    cout << "I eat like a fish!\n";
            }
        };
        class GoldFish : public Fish {
            public:
                void eat() {
            cout << "I eat like a goldfish!\n";
            }
     };
int main() {
    Animal animal;
    Wolf wolf;
    Fish fish;
    GoldFish goldfish;
    animal.eat();
    wolf.eat();
    fish.eat();
    goldfish.eat();
    return 0;
}

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The output is :-
I eat like a generic animal.
I eat like a wolf!
I eat like a fish!
I eat like a goldfish!

Instead of this:-

I eat like a generic animal.
I eat like a generic animal.
I eat like a generic animal.
I eat like a generic animal.

Why is this happening? Is there something wrong? If it is possible then what is the use of this virtual function. Please answer me.

Thank You.