Crush the head of a snake after killing it

Superstition says that one should crush the head of a snake after killing it otherwise its kin might find an image in its eyes and seek revenge. 
In fact the reason is that a snake can bite or kill a person even with a detached head and in order to completely neutralize it, it is necessary to crush its head. Also, being a cold-blooded organism, even if some of its vital organs stop working it will stay alive for hours and die a slow and painful death. So it is recommended to crush its head to give it a quick and painless death.