A phrase coined by environmentalist when they try to persuade children not to dump litter on their hilly nature reserve. Originated from the horror story by Wes Craven called 'The Hills Have Eyes'. Environmentalists use this phrase in reference to the flesh-eating mutants in the book so that the children are too scared to dump litter because they live in fear of the mutants seeing it and going after them to eat them.
Environmentalist: Now, children, don't you go dumping any of your litter in our lovely hills because the hills have eyes - eyes to watch you! Those eyes belong to flesh-eating mutants!