interface Talkative {
    public function talk();
}
class Cat implements Talkative {
    public function talk() {
        return 'Woof' . PHP_EOL;
    }
}
class Dog implements Talkative {
    public function talk() {
        return 'Meow' . PHP_EOL;
    }
}
class Tortoise implements Talkative {
    public function talk() {
        return 'Yak yak yak yak ...' . PHP_EOL;
    }
}

$cat = new Cat;
$dog = new Dog;
$tortoise = new Tortoise;

echo $cat->talk();
echo $dog->talk();
echo $tortoise->talk();