you were in posion class and the truth is you weren't paying attention, you were lost in your thoughts until Snape asks you to smell the posion*

"I can't, Draco's perfume stinks and he won't let me smell it."

Draco looked at you with contempt and did not remain silent, getting up quickly

"It's your perfume that stinks everywhere"

said angrily until Professor Snape tells them that it is "amortenia" they both looked at each other in astonishment while some students laughed