As mentioned I do postcrossing. In my wish list (user soikkis) there are cards with cows, birds, butterflies and dragonflies. Birds, butterflies and dragonflies - I photograph them and enjoy that a lot. One part of the joy is trying to recognize what bird/butterfly/dragonfly there is in a photo.
But cows! Maybe I like cows because I lived in a little farm in childhood. But look at this cow in card I received - who could say no to that face.