Now, that being said, don’t go overboard—you don’t want your characters mumbling, chirping, drawling, squeaking, yelling, and hissing all through your book.
But an occasional action verb can add nuance to the dialogue by telling the reader how the line is said.
“If you keep it up, I’m going to smack you,” she hissed.
Here, the character is trying to not let people know she’s upset by pitching her voice down but still trying to convey her displeasure.
“If you keep it up, I’m going to smack you,” she bellowed.
The character has reached a point where she doesn’t care who hears her and wants the person she’s yelling at to stop whatever they’re doing.
“If you keep it up, I’m going to smack you,” she sang.
Here, the character is talking to a person old enough to realize the threat of her words even though the tone is sweet.
In each line, the atmosphere and flavor of the dialogue exchange changes depending on how the character says that line.