Phantom poops

I hate when I'm driving and I get a whiff of Charlie's poop. I immediately think "do I have it stuck on me?" and the answer is (so far) always "no". Why on earth do I get struck with these phantom poops? Sometimes they hit Eric too but they hit me often and at random times. Once, I was so convinced he pooped that when I opened his diaper and there wasn't any I stood there for a minute confused.