NATURE: "PETS: WILD AT HEART"
PBS, 8:00 p.m. ET
Part 2 of 2. This concluding installment is called Secretive Creatures, and it explains some of the hidden ways animals relate to one another, and react to things and people around them. Cats with catnip. Goldfish flirting by rippling through the water. And why, when horses in stables are groomed, it’s welcomed as a calming and affectionate activity. Check local listings.