Dogs can sniff out cancers, bacteria such as C diff, bed bugs, low blood sugar (before severe symptoms hit) along with the stuff everyone knows about like drugs, bombs, lost humans, etc. I remember reading years ago about a dog that kept sniffing at a spot on a person (can't remember now if the dog was being trained for cancer detection or if it was the person's dog), doctor removed a piece, pathology said it was nothing, the dog still kept going for the spot, they removed the whole thing and it was melanoma. I've read of pet dogs picking up on breast and other tumors in their humans too. They are amazing creatures with amazing noses.