private function pruneUses($subject)
    {
        $repository = $this->entityManager->getRepository(UsedString::class);
        $usedStrings = $repository->findBy(['subject' => $subject], ['id' => 'desc']);

        // IF there are extra used strings, prune the extras
        if (count($usedStrings) > $this->maxReuse) {
            array_map([$this->entityManager, 'remove'], array_slice($usedStrings, $this->maxReuse));
            $this->entityManager->flush();
        }
    }