When I think of the word "simultaneous," I never fail to hear Chef from
South Park in my mind.
And while I enjoyed
South Park once upon a time, and Chef's song "Simultaneous" cracks me up, I'm not referring to the simultaneous action Chef is referring to. I'm thinking about simultaneous actions characters perform -- or attempt to perform -- in narrative prose.
Simultaneous action is the term I use in edits when an author has a character do something that's physically impossible or when a character does two things at one time. For example:
Walking through the kitchen, Jana emptied the trash can.
Jana can walk through the kitchen, yes, and Jana can empty the trash can, but Jana cannot perform both of these tasks simultaneously. (This is a bad example because I cannot correct the simultaneous actions without completely rewriting the sentence.)
Here's a better example:
Pulling out of the driveway, he drove down the street.
The aforementioned "he" cannot pull out of the driveway and drive down the street at the same time, so a better way to rewrite this sentence to avoid simultaneous actions would be:
He pulled out of the driveway, then drove down the street.
As I hope you can see, the leading cause of simultaneous actions occurs when
-ing verbs are used at the beginning of a sentence. Once begun, it's a difficult writing crutch to break, but I think if a writer is aware during the drafting or self-editing phases, the problem of simultaneous action is easy to manage.