Seizure response dog
Certain kinds of dogs are able to predict that a person is about to have an epileptic seizure.  This gives the person time to get to a safe place before the seizure starts.  Usually, people say that dogs develop this behavior spontaneously (on their own), or over some time. There have been some studies where dogs were trained to alert to seizures when they were given rewards for correctly predicting seizures - but these studies were only partly successful.  Some untrained dogs may help their owners during a seizure, but there are also reports of dogs that have reacted aggressively or even died as a result of witnessing or anticipating their owner's seizure.