"No, I'm not a mall . . . ninja," was his reply. I found myself trying to figure out what the ellipses were meant to convey. This is why the best writers read their work aloud early in the process . . . . hearing it spoken will alert you to mistakes, even small mistakes of emphasis, that your brain would gloss over if you were reading silently. His pause was . . . interesting. I found myself wondering where the emphasis was supposed to be, because it makes a difference. Observe:
"No, I'm not a mall ninja," he said with the cool sternness of a rottweiler contemplating a squirrel. Where did these little punks pick up this ridiculous lingo?
"No, I'm not a mall ninja," he said with the cool sternness of a rottweiler contemplating a squirrel. It was beginning to seem likely that he'd have to kill another one. Hatsumi would be displeased.
See what I'm saying? Punctuation, kids. Emphasis. Learn it, love it, live it.