When Penny nudges me I usually assume it's because she wants something. However, it often makes me think about the stories you hear about dogs that can sense a problem before a human can.
On Itchmo I read a story today about a dog that has enabled a young girl with epilepsy to lead a more independent life because he can give her five to ten minutes warning that she is about to have a seizure. The great thing, in my opinion, is that the dog was already living with her for four years before she was diagnosed and so the bond between them is based on pre-existing mutual love and doesn't just stem from her gratitude for his usefulness to her. She had rescued him from possible starvation when he was the runt of a litter and now he repays that debt each day.
There's another story in The Cairns Post about a neglected and possibly doomed dog that was rescued. He also has repaid the debt magnificently by saving the family's baby from a snake.
At ABC News there's a discussion by Nicholas Dodman, director of the Animal Behavior Clinic at the Tufts Cummings School of Veterinary Medicine in Massachusetts about what might be going on when a dog warns a human of an impending medical crisis, like a seizure or a diabetic's low-blood-sugar event. Apparently scientists have found no evidence that dogs can sense changes in human brainwaves, but Dodman writes that there is still plenty of anecdotal evidence that dogs use some sort of cues to predict problems before they happen.