5. When he smells a hint of your perfume in passing.
Perfume has a similar effect as natural pheromones, and in some cases, it can drive men crazy. It is more effective to wear just a hint of perfume so as not to smell as if you have bathed in it. If you end up using too much, it will have an adverse effect on men. The rule of thumb is to leave a hint of scent in passing and not a trail behind you—that will leave a lasting impression on his senses.