[UserNameGoesHere]

Okay Reincarnate, I made some code for you :-P

#include <iostream>

class Animal {
public:
Animal();
~Animal();
/*virtual*/ void make_sound();
};

class Cat : public Animal {
public:
Cat();
~Cat();
void make_sound();
};

Animal::Animal(){}
Animal::~Animal(){}

void Animal::make_sound(){
	std::cout << "ROAAAAARRRR" << std::endl;
}

Cat::Cat(){}
Cat::~Cat(){}

void Cat::make_sound(){
	std::cout << "Meow" << std::endl;
}

int main(int argc, char* argv[]){
	std::cout << "Testing animals" << std::endl;
	
	Animal* animal = new Animal();
	Cat* cat = new Cat();
	Animal* catanimal = dynamic_cast<Animal*>(new Cat());

	std::cout << "animal says "; animal->make_sound();
	std::cout << "cat says "; cat->make_sound();
	std::cout << "catanimal says "; catanimal->make_sound();

	delete animal;
	delete cat;
	delete catanimal;

	return 0;
}

If you declare without the virtual keyword (as is above, where it is commented-out) you get as output

Testing animals
animal says ROAAAAARRRR
cat says Meow
catanimal says ROAAAAARRRR

But if you do declare the virtual keyword (remove the commenting) you get as output

Testing animals
animal says ROAAAAARRRR
cat says Meow
catanimal says Meow

Or, basically, yes the virtual keyword does matter a whole lot, and FissionMailed is right.