PHP Hush Little Baby

Lullaby.php

<?php

class Lullaby
{
    /**
     * @var HumanoidInterface
     */
    private $littleBaby;
    /**
     * @var HumanoidInterface
     */
    private $papa;
    /**
     * @var ContainerInterface
     */
    private $rewards;
    /**
     * @var HumanoidCollectionInterface
     */
    private $town;


    private const EVENTS = [
        'mockingbird.wont_sing' => 'diamond_ring',
        'diamond_ring.turns_brass' => 'looking_glass',
        'looking_glass.gets_broke' => 'billy_goat',
        'billy_goat.wont_pull' => 'cart_and_bull',
        'cart_and_bull.turn_over' => 'dog_named_rover',
        'dog_named_rover.wont_bark' => 'horse_and_cart',
        'horse_and_cart.fall_down' => null,
    ];
    /**
     * @var EventBroadCasterInterface
     */
    private $eventBroadcaster;

    public function __construct(
        HumanoidInterface $littleBaby,
        ContainerInterface $rewards,
        HumanoidCollectionInterface $town,
        EventBroadCasterInterface $eventBroadcaster
    )
    {

        $this->littleBaby = $littleBaby;
        $this->papa = $littleBaby->getParent();
        $this->rewards = $rewards;
        $this->town = $town;

        $this->eventBroadcaster = $eventBroadcaster;
    }

    function hush()
    {
        ob_start(); // Don't say a word
        $this->papa->buy($this->rewards->get('mockingbird'));

        array_walk($events, function ($value, $eventName) {
            $this->eventBroadcaster->on($eventName, function () use ($eventName, $value) {
                if (!array_key_exists($eventName, self::EVENTS)) {
                    return;
                }
                $reward = self::EVENTS[$eventName];
                if (null !== $reward) {
                    $this->papa->buy($this->rewards->get($reward));
                } else {
                    $this->town->setSweetestBaby($this->littleBaby);
                }
            });
        });

        ob_end_clean();
    }
}