Another way dogs protect and save is by sniffing out and detecting diseases in humans. There’s no denying dogs have a killer sense of smell. It’s actually 100,000 times more sensitive than ours. Dogs are capable of smelling everything from drugs to electricity to underground gas pipes and ovulating animals. But, the most amazing things dogs can sniff out are cancer, epilepsy and diabetes. By just smelling a patient’s urine, they can sniff out bladder cancer and they can diagnose early and late lung and breast cancer by smelling your breath. Dogs have also helped discover ovarian cancer and skin cancer since affected cells give off a different smell than healthy ones. (source)
The true reason for the attraction between Hannibal and Will is that Hannibal was a dog in his previous life.