Many things can spoil a wine's flavour and make it fault. The most obvious is cork taint, where a must-smelling cork causes the wine that comes into contact with it to taste musty too (or sometimes just to taste flat and dull). Hydrogen sulphide is a compound that can be produced during fermentation and, although eradicable, can sometimes make it into bottle; you'll detect it as a farmyardy, eggy smell. And volatile acidity, while tolerable in small amounts (and can actually help to lift a wine's aroma), can also spoil a wine with its vinegary or nail-polish-remover smell if present in large dowse.