There's a characteristic smell of a cadaver when the person has been poisoned by cyanide--almonds, I think. Pat Cornwell uses it in one of her books, and it was Jonas Salk's early claim to fame among his peers: he smelled it on someone brought into the emergency room. From then on, the other doctors would call him over to smell the patients when they came in so they could make the diagnosis.
Yes, almonds. Some info on cyanide here: http://www.freerepublic.com/focus/f-chat/1510878/posts?page=42#42