<?php

abstract class Animal {
    abstract public function makeNoise();
}

class Dog extends Animal {
    public function makeNoise() {
        echo 'Woof'. PHP_EOL;
    }
}

class Cat extends Animal {
    public function makeNoise() {
        echo 'Meow' . PHP_EOL;
    }
}

$dog = new Dog;
$cat = new Cat;
$dog->makeNoise();
$cat->makeNoise();