There was an upswing in pet memoirs in the past few years, from Dewey: The Small-Town Library Cat Who Touched the World to Marley & Me. Sure, Marley & Me was billed as an autobiographical novel, but still, it was based on the author's real life. While the trend has slowed recently, I was wondering why we haven't seen any fiction about pets.
Where is the great pet novel? There are some classic children's tales about pets, but when it comes to truly adult literature, the list is thin. In fact, sitting here typing, I can't really think of any truly classic literature with a pet as a major secondary character - at least not any non-anthropomorphic pets.
Wait, no. Old Yeller. Still pretty much a children's story, though.
Write a story where the main secondary character is the main character's pet.
Why do I suggest this prompt? Frankly, because I think it's fun. And limiting yourself to your own pet means limiting your story. Take every story you've ever heard about pets and create a truly wonderful pet story - whether or not the pet is well-behaved or not.
And yes, the ending will probably be a tearjearker, unless your chosen pet is a turtle.