Most people – including scientists – assumed we can't just sniff out danger. It was thought that we become afraid of an odor – such as leaking gas – only after information about a scary scent is processed by our brain. But neuroscientists at Rutgers University studying the olfactory – sense of smell – system in mice have discovered that this fear reaction can occur at the sensory level, even before the brain has the opportunity to interpret that the odor could mean trouble.
— Read more at Sniffing out danger: Rutgers scientists say fearful memories can trigger heightened sense of smell at Science Codex.