She looks like a pretty woman, usually wearing a white kimono, like most ghosts. Her mouth has been slit from ear to ear, so that there is a very large scar on her face. Sometimes the mouth itself is very wide and holds many short pointy teeth.
The Kuchisake-onna is the vengeful spirit of a woman who mainly targets children. She is said to be cold and cruel - but also more or less easily confused.
According to the legend, children walking alone at night may encounter a woman wearing a mask or a scarf - or sometimes holding a fan to her face - that hides her mouth. The woman will stop the child and ask ; "Am I beautiful?" If the child answers no, the child is killed with a pair of scissors or a blade which the woman carries. If the child answers yes, the woman pulls away the mask/scarf/fan, revealing that her mouth is slit from ear to ear, and asks ; "How about now?". If the child answers no, he/she will be cut in half. If the child answers yes, then she will slit his/her mouth like hers.
It is near impossible to run away from her, as she will simply reappear in front of the victim. It is said she does this because of some marital issues - she is a woman who was mutilated by a jealous husband and returned as a malicious spirit.[http://en.wikipedia.org/wiki/Onry%C5%8D ]
It is said that throwing fruits or candies at her (so she will pick them up) or answering with something neutral might buy the victim enough time to flee, though, as she is distracted or confused.