I once did a project with a well known food company - met a young woman whose sense of smell was just bizarre. She was also a trained food chemist, so by sniffing a bottle of juice or a bottle of tea, could tell which flavor chemicals were added in approx. what proportions. off-notes or variances that were imperceptible to others stood out like a beacon to her.
Must be what is like to be a dog. They just have to look at people and say “really? You can’t smell that?”