Scent is the most instinctive of the senses. We react to scent in a way that's defined by the exact molecule. No other molecule can create that particular scent, and no other scent can cause that particular reaction in our system.
That's why different scents mean specific things to us. A scent is a personal anchor point for the memories associated with it, and it operates with molecular precision. Our perception of scent is led directly to our most basic brain functions, and we react instinctively to it. It completely bypasses any cognitive function.
As a writer, scent is a sure way to trigger instinctive reaction of your characters. You don't have to explain anything. Just add scent, and let the story unfold from there.
In this exercise you are going to take two different angles to it.