Short answers, pulled from the story.
The human nose can distinguish over one trillion unique odors. This capacity dwarfs the previous estimate of ten thousand and reveals a sensory world far more complex than conventional wisdom suggests.
Linda B. Buck and Richard Axel were awarded the Nobel Prize in 2004 for their groundbreaking work on the sense of smell. Their research demonstrated that each odor receptor molecule recognizes only a particular molecular feature, functioning like a key fitting into a lock.
The olfactory system is the only sensory system that bypasses the thalamus to connect directly to the forebrain. This direct pathway allows for immediate and powerful emotional responses by sending signals straight to the amygdala and hippocampus.
The bloodhound has a sense of smell that is ten- to one-hundred-million times more sensitive than a human's. This capability allows the bloodhound to detect a scent trail a few days old.
The sense of smell influences the partners we choose by allowing humans to detect MHC genes of potential sex partners. This mechanism helps avoid inbreeding and ensures the genetic diversity of offspring.
About 50% of patients with SARS-CoV-2 experience some type of disorder associated with their sense of smell. These disorders include anosmia and parosmia, a distortion in the perception of an odor.