Pediophobia is a fear of dolls or similar objects. Psychologist Ernst Jentsch theorized that uncanny feelings arise when there is an intellectual uncertainty about whether an object is alive or not. Sigmund Freud further developed on these theories. Japanese roboticist Masahiro Mori expanded on these theories to develop the uncanny valley hypothesis: if an object is obviously enough non-human, its human characteristics will stand out and be endearing; however, if that object reaches a certain threshold of human-like appearance, its non-human characteristics will stand out, and be disturbing.