If you scare someone so much they can't move, you petrify them. Petrify is to make something like a stone or to literally turn to stone.
At the heart of the word petrify is the Latin word petra which means "stone." In the scientific sense, wood petrifies in an environment without oxygen, say when it is buried by lava, and minerals such as silica enter the wood and fill the cells, making it hard as stone. More commonly, something petrifies a person or an animal when it scares them very much. During thunderstorms, the dog is so petrified that it hides under the bed. If you are in a store when it is being robbed, you might be petrified too.