Kurumi's potion was bubbling a lot more than the others around her and was sort of giving off an eerie looking purple smoke that sort of went by unnoticed if you were not looking carefully - which the Gryffindor was not - and instead had her eyes focused on her mortar and pestle as she attempted to grind her fangs into powder. When she eventually got it into a powder, mostly anyway, Kurumi sprinkled it in and then reached for her cinnamon stick to begin grating it into the cauldron.
*ACHOO*
Cinnamon had such a strong smell...Kurumi liked it the smell, especially since it reminded her of baking, but grating it all fresh like this and in such close proximity to her nose was making her sneeze.