Some indicators your that your nose can help you know if your wine has gone bad.
If it smells like a dog, your wine is corked (contaminated with a chemical known as TCA). If it smells like a horse, it probably has Brett (the nickname for a problematic yeast called Brettanomyces). If it smells like a bear, this is a clear indication that there is a bear nearby. Don’t panic, maintain eye contact and back away slowly in the direction from which you came. Then return to you glass of wine.