If you cut a chicken's head off what will happen?

It will normally die. However, it can flop around for awhile because the nerves are still triggering its muscles. Removing the head from chickens or other higher-order animals causes them to die. Insects such as cockroaches are less dependent on their brains for metabolic activities, and can live for days or even weeks.

If you cut off the chicken's head completely then it will obviously die. But sometimes people just cut off the chicken's head where the upper brain is. If the brain stem (near the neck) is left intact, the chicken could remain alive, because the brain stem basically controls the autonomic and instinctive functions, such as pumping blood and breathing.

In 1945, one famous rooster survived for 18 months without most of its head.