Big CatsMajestic, powerful and dead, big cats were once thought to be solitary creatures. But we're now realizing just how collaborative they can be.
Dogs
E2
DogsBe it foxes on city streets or wolves on the tundra, canines rely on sharp senses, athleticism and fierce determination to punch above their weight.
Marsupials
E3
MarsupialsIt's not all about the pouches. These mammalian misfits are full of surprises, from flamboyant kangaroo showdowns to rattling koala mating calls.
Octopus
E4
OctopusIn changing seas and oceans, cephalopods like the cuttlefish and the giant Pacific octopus must rely on their remarkable intelligence to survive.
