Using Setting in Dialogue
In real life, conversations usually have a lot of pauses - especially emotionally charged conversations. In fiction, much of the dialogue occurs in emotionally charged situations. A rapid exchange of comment and response will not ring true in this case. Adding, "he paused" or "She thought a bit" is fine once in a while, but that gets over used quickly.
One of the things I do to handle this is have my character's interact with their environment to show the pause or thinking occurring.
In "Love, Sex, and Understanding the Universe," during a very intense scene in a coffee shop when Jim, my main character, reveals he's bisexual to someone very important to him who's homophobic, I breakup dialogue and show his discomfort by having him feel the granules in a packet of sugar. In the same scene I have the person he's talking to stare fixedly at a car parked on the curb. I also show Jim gripping the edge of the saucer at one point, later, he's looking at the cold slosh at the bottom of his cup.
In "Bonita Verses Ivan Rastaman and the Monkey-Go-Round," I have Bonnie's mother accidentally singeing the blouse she's ironing for work when Bonnie asks her if she'd been a planned child.
The trick is to intersperse dialogue with body language at key moments. This also has the handy effect of creating suspense for the readers - keeping them waiting just a bit for what's going to be said next.