Cats are predators and have an instinctive need to act out their natural cycle of hunt → eat → groom/bathe → sleep. Without opportunities to fulfill this instinct, cats are more likely to act in a predatory-fashion toward people and other pets. If your cat is stalking another cat, attacking your feet while you're in bed sleeping, or nipping at your ankles before darting again, your cat likely needs more play opportunities!
Why Prey Play?
Why do I choose the words "prey play" instead of "predatory play"? My preferred way to encourage cats to act out their predatory instincts is through interactive wand-toy play with their owners. Your role in this isn't to have the wand toy act as a predator toward your cat; your role is to have the wand toy act as a PREY animal. Cats normally hunt bugs, small rodents (such as mice, chipmunks, etc.), rabbits, birds, and sometimes even snakes and squirrels. Try to embody one of these prey animals through the wand-toy. Would a mouse dive-bomb your cat from above and run along its belly? Not likely. Would a bird run along the floor and tap your cat's tail? Also unlikely. If you need inspiration, watch nature videos of these animals to develop a sense for how they move and hide. Geek inspiration: Remember the famous "Don't Blink" Doctor Who episode? You can try only moving the toy when your cat is looking away. This can be a great way to catch their attention!
TIP: Watch your cat's whiskers, tails, and eyes during prey play!