Here's something that should stop you cold: humans are the only animals on Earth that cry emotional tears. Not tears to clean the eyes, not tears from irritation, but tears from joy, from grief, from being overwhelmed by beauty. Elephants mourn their dead without weeping. Dolphins recognize themselves in mirrors without crying at their own reflection. Your dog, who seems to love you completely, has never shed a single emotional tear. This is not speculation. This is measured fact. And nobody knows why.