Yes, the silent, and often mysterious killer. Of course I saw the most cases of CO poisoning, when I was working in charity type of hospitals--where we had unknowns off the street or highway. Of course lab tests are much better now than 50 years ago, but often it was a person who was unconscious with no history. In several cases we were able to trace it down to a car with a leaky muffler. CO used to be in vogue for suicide--when I was a teen one of the neighbors died that way in his garage.