What are verbals, you ask. They are those verbal phrases which don't function as the verb in a clause, they act like nouns or adjectives or adverbs. Go get your grammar book out and look it up for the full definition.
The ones that were giving me the most fits were the present participles (the -ing form of the verb). Sometimes, they need a comma, sometimes they don't. But, do any of the THREE grammar books that I have adequately explain when they do and when they don't? ... Nooooooo ....
It's a present participle after a verb. One would think that it would always be the same. But, it isn't because it depends on what that participial phrase is doing after the verb. Is it acting like a noun, an adverb, or an adjective. Is it the subject complement, direct object or object of a preposition?
I'll toss some sentences out to illustrate my confusion.
He walked dragging his foot behind him.
He walked, gazing at the sunset.
He said, weeping into his handkerchief.
He said spraying spit everywhere.
Fear not. I did read this helpful bit regarding commas in "Eats, shoots & Leaves" by Lynne Truss: "This is why grown men have knock-down fights over the comma in editorial offices ..." Well, hell, if grown men are getting into knock-down fights over the comman, it's no wonder I feel like my brain has imploded.
Perhaps, the most interesting and important point of what I have learned in the editing process is this: If the story grabs the readers attention, they won't notice the punctuation. So, it really doesn't matter if I put a comma in front of that present participle or take it out. Unless they are grammar nazis, the reader will not notice. And even if they are, they might not agree with the rules that I learned and am using for proper punctuation.