She has green eyes and often wears baggy blue jeans and sneakers with her trademark yellow moon-shirt. She has curly red hair, held with a crescent moon clip, and always wears crescent shaped glasses, except once instance when only one lens is covering her eye (skiing accident). Mary has been shown to be more compassionate than Susan. Mary is prone to believing in less in science and more in the realm of science fiction, which proves to be correct, despite the scorn received from her twin. Mary seems to be more level-headed and conservative than Susan, and speaks her mind much less often.