Smell...one of our senses we often ignore unless there is something particularly pleasant or gross in the air.
However, your nose knows more than you think.
For example, did you know that a study was done that shows "people deemed to be at ultra high risk of developing psychosis and found those that went on to develop schizophrenia, rather than other forms of psychosis, all displayed the inability to identify smells."
Or that the lack of being able to smell can be symptomatic of other diseases like Parkinson's?
And what about aromatherapy? Pheromones? Memories? Your nose can tell you a lot!