"Sh smiles. Her teeth aren't chattering because she is cold... they are moving about inside her mouth, her gums twisting as the teeth shift about. They rise and recede as you watch, chattering as they rattle against each other." --Planescape: Torment.
Planescape: Torment is one of my favorite games, and the quotation above is a reason why. One small subquest you can go on starts when you run into Ingress, a woman with a troubled past. Forty years ago, she was whistling a certain tune while she walked under an arch formed by two dead trees, and found herself in Sigil, the City at the center of existence. In Sigil, every enclosed space is potentially a portal that can lead you elsewhere when you cross its threshold, as long as you have the right key--and as Ingress learned, there's more than one definition of "key." She tried to get back home by opening portals, but couldn't find the right one--and some led her to places so warping that she herself isn't quite sane or human any more, as demonstrated by the quotation above. It's a nice moment--her teeth keep chattering during your whole conversation with her, and she slowly reveals more and more, until you're willing to dismiss her as insane, especially when she says that her fear of winding up somewhere worse has kept her from going indoors for the past thirty years, or even leaving the Square she's in--no crossing thresholds of any kind. And then she opens her mouth, and you realize she may have the right idea...