Agreed with the above posters.

Destroying the brain with a mallet is brutal and might look horrifying but it is an instantaneous humane death. Be aware that the body may still thrash and move, but that is because the brain has been destroyed and the body is spasming. It does not mean the snake is still "alive". With snakes, the heart can even beat for a long time after you destroy or remove the head, but as long as the brain is destroyed, the snake is not alive and is not feeling anything.