Robert S. Hichens said this quote

For great changes in the human mind are terrible. As we realize them we realize the limitless possibilities of sinister deeds that lie hidden in every human being. A little child that loves a doll can become an old, crafty, secret murderer. How horrible! And perhaps it is still more horrible to think that, while the human envelope remains totally unchanged, every word of the letter within may become altered, and a message of peace fade into a sentence of death.