protected function getResponse(TwitterBot $bot, $tweet)
 {
     $id = $tweet->id_str;
     $sender = $tweet->user->screen_name;
     $targetId = $tweet->in_reply_to_status_id;
     $text = $tweet->text;
     $username = $bot->getUsername();
     if (strpos($text, '@' . $username) !== 0) {
         return null;
         // not a direct mention
     }
     $game = SpymasterGame::getByTweetId($targetId);
     if ($game === null) {
         return null;
         // Not in response to a game
     }
     if ($game->getFinished()) {
         return 'Sorry, this game has already finished. DM me "start" to start a new game of your own';
     }
     $text = substr($text, strlen($username) + 2);
     $text = preg_replace('/[^A-Za-z]+/', ' ', $text);
     $words = explode(' ', trim($text));
     // TODO: validate this shit
     $game->recordGuess($sender, $words);
 }