My dog comes in from a long walk, tongue hanging out, panting. She heads immediately to her water dish and starts lapping hungrily. I stop her, pick up the dish and replace the old, warm water with fresh cold water and return the dish to her. She resumes lapping up the water with the same enthusiasm as before. And it occurs to me that the fresh cold water thrills me more than her. In fact, I don’t even think she notices. Then I remember. This dog drinks skanky standing water from still puddles she finds on our walks. Clearly being disciminatory is not in her nature.