Which consequence can result from untreated tetanus?

The correct choice highlights the primary consequence of untreated tetanus, known for causing severe muscle contractions and rigidity throughout the body. Tetanus, caused by a toxin produced by the bacterium Clostridium tetani, affects the nervous system, leading to prolonged muscle contractions that can result in a state of stiffness, particularly in the jaw area, which is why the condition is often referred to as "lockjaw." This rigidity can be extremely painful and can extend to the spine and other muscular regions, significantly impacting mobility and causing respiratory difficulties if the muscles that control breathing are affected.

The other options do not align with the hallmark symptoms of tetanus. For instance, skin rashes typically relate to allergic reactions or other dermatological conditions rather than infections like tetanus. Heart palpitations can indicate various cardiovascular issues but are not associated with the muscular and neurological disturbances caused by tetanus. Chronic headaches might arise from different health conditions but are not a direct effect of untamed tetanus infection.