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