If your dog shows unusual dislike towards someone, he is making you aware about the potential threat that person can present to you.
Serious diseases in humans: Dogs are capable of detecting cancer, even when it is at stage zero.
Researches have found that cancer tissue release particular chemical that is different to normal tissue, and dogs are surprisingly good at recognizing the difference between malignant tissue and normal tissue. A woman from California noticed that her dog used to lick her right breast, and when she went to doctor she was diagnosed with breast cancer. In a research, a trained Labrador retriever was able to successfully detect colon cancer in people with more than 90 % accuracy rate.
Not only cancer, your dog can alarm you when you have low blood sugar and seizures.
Pregnancy: Although, there is no concrete scientific evidence that proves that dogs are capable of sensing pregnancy, so many examples prove it. Dog's ability to read human body language, smell, and behavior helps him to detect pregnancy. Certain changes happen in the odor, body shape, body language, mood and behavior of pregnant woman which dog can read easily.