"Them!" is not a short! Why is that the only choice? I don't think you've riffed it before...

It's a movie starring James Whitmore and Edmund Gwenn (Santa Clause from Miracle on 34th Street!)

1) Giant ants (Some of the fly)
2) The Thing (James Arnes)
3)It's a toss up between the LA sewer system and Fess Parker

http://www.imdb.com/title/tt0047573/

The famous giant ant movie riffed on the big screen. What more can I say.