It's Oliver's birthday, and everyone but him wants to celebrate. It also (coincidentally) happens to be Arnold's birthday too. Everyone tries to persuade Oliver to get Arnold a birthday present, while he thinks he deserves one because he's human, while Arnold isn't. It turns out Arnold, and Lisa are the only one's who get Oliver a gift, and when he and Lisa go over to the Ziffel's house for his party, only to find that there wasn't one, they return to find all of their furniture stolen. (thetvdb.com)