Yes, this completely normal reaction is usually a natural response to feeling threatened, scared, or agitated. This "puffed-up" appearance is caused by the involuntary contraction of muscles, making it appear larger and more intimidating to potential threats. It's a common behavior observed in cats when they feel threatened by other animals, unfamiliar people, or loud noises. While it's a normal reaction, prolonged puffing up or frequent occurrences without an apparent trigger could indicate underlying stress or anxiety, warranting further attention and possibly intervention from a veterinarian or animal behaviorist.