About attacking ankles
From 101 Questions Your Cat Would Ask Its Vet If Your Cat Could Talk by Bruce Fogle
Cats who stalk their owners are bored, frustrated felines. They need mental and physical stimulation and are almost always housebound animals. With nothing much to do, they sleep most of the day.
The only other living things that these cats ever see are humans....human movement can be exciting. Human feet move erratically, just the way real prey moves. They start, stop, turn, back up, move forward,...,disappear around corners....They become the most exciting thing in a boring existence.
With little else to do, some cats stalk feet....he slinks low to the ground, unblinkingly staring at his prey. As the feet move through the room, the cat quietly stalks forward. Suddenly he launches his attack....Grabbing with his forepaws and kicking with his hind legs, he grasps the ankle and sinks his teeth into the flesh. In a flash he is gone.
The only way cats can overcome this form of hunting aggression is to develop an alternative release....People who don't enjoy this behavior either should wear high protective leather boots or should play more games with their captive moggies.