when you are talking to a female professor of yours you can use this for comic relief. it is joke on on using the word professor to call both female and male humans ;) by specifying using "ess".
you go to her and say:
-"Excuse me, professor..ess"
-"Just professor, a-thank you very much"
as if there's a female version of professor like there is in latin languages
e.g professora, professor
> professor Linda: can i help you?
> Charlie Student: oh hi, professoress, or are you a doctor-ess already? did you ever get you're phd?