1
There's an idiom "rub something in someone's face".
For instance,
I really screwed up my speech, and Caroline keeps rubbing the disaster in my face.
(https://www.idiomsandslang.com/rub-something-in-someones-face/)
Your ex is rubbing a new relationship in your face?
(https://hackspirit.com/ex-rubbing-new-relationship-in-my-face/)
Therefore, if I want to say "rubbing our relationship in their face(s)", should I use "face" or "face(s)"?
2
I read the sentence:
When cats rub their face or tail against humans, other animals, or household items, they are leaving behind this pheromone that they can identify.
(https://www.petmd.com/cat/behavior/why-do-cats-rub-against-you)
Why are "face", "tail" and "this pheromone" all singular?