I heard a story a while back about a guy who evidently cared for his dog quite a bit.  When he passed away, in his will he left his ex-wife an income of $10,000 per year, but only as long as his dog survived.  After that, the money would stop.
I’m not sure how apocryphal that story is, though it certainly sounds unlikely.  On the other hand, there really is a fellow up in Hagerstown who passed away recently and left his entire $800,000 estate to his dogs.