Say I want to write something to say:
John looked over his shoulder as he opened the door slowly.
However, for stylistic reasons I don't really want to use as in that sentence. There must be other ways of expressing simultaneity. What words or phrasing could replace the as in that sentence?
The Help Center here says
To prevent your question from being flagged and possibly removed, avoid asking subjective questions where every answer is equally valid: “What’s your favorite ______?”
... so please explain your choice and why your suggestion works [e.g. its grammar] as that introduces some objective measure of validity.