The em-dash alone is not an LLM-reveal -- it's how the em-dash is used to pace a sentence. In my experience, with an LLM, em-dashes are used to even pacing; for humans (and certainly, for me!), the em-dash is used to deliberately change pacing -- to introduce a pause (like that one!), followed by a bit of a (metaphorical) punch. The goal is to have you read the sentence as I would read it -- and I think if you have heard me speak, you can hear me in my writing.