Allison is allergic to the perfume, so she starts sneezing, her nose starts running, and her eyes water
Now, everytime Allison smells someone's perfume, she gets nervous that she will have another allergic reaction.
Generalization: Allison gets nervous anytime she smells any type of perfume.
Extinction: After a while, Allison smells lots of perfume without having any reaction, so her fear eventually goes away
Spontaneous Recovery: Then, one day, someone sprays the same perfume again in the hall, causing Allison to have another allergic reaction. This causes Allison's fear and nervousness around perfume to return.