Smell that letter, a synesthesia experiment
For a small percentage of the population, letters or numbers are associated with particular smells or colors; words have flavors, sounds are perceived in color, numbers exist in a mental spatial pattern, or ordered objects have their own unique personalities.
Synesthesia is a neurological condition that results in a difference in perception; it's not exactly a disorder or a disease since it doesn't necessarily have negative consequences--in fact, it could be a positive thing. Imagine if everytime you saw the color blue you experienced a pleasant scent.
Checkout these fun experiments on synesthesia and decide for yourself the color of a lion's roar: