As strange as it may seem, this kind of reaction is more common than you’d think. While humans rely heavily on sight, cats (and dogs too!) experience the world primarily through scent. If your boyfriend has picked up unfamiliar smells (especially those of other animals, including other cats) your cat might not immediately recognize him. This can understandably spook some felines, but with a little patience and reassurance, cats can learn to adjust and calm down.