Police are investigating after a pit bull viciously attacked a woman on a New York City subway last week. On Friday, a straphanger was standing on the 4 train when the dog, which was on the owner’s leash, latched onto the rider’s foot and would not let go. Other riders tried to free the woman’s foot from the dog’s tightly-clenched mouth. Authorities are now trying to identify the dog's owner. One veterinarian explained how you could escape a dog’s attack in such a closed space.