CARRY SANDERS: For two days, all 15-year-old, David Yepes, has heard and thought about are his injuries from the second explosion.
WOMAN: This is remarkable.
CARRY SANDERS: But, today, David smiled.
DAVID: Yeah, we have a dog at home, but he's a small Yorkie terrier.
CARRY SANDERS: For just a moment, Luther and Ruthie made the shrapnel that tore through his left leg and the painful second degree burns almost an afterthought.
DAVID: It's relaxing, it kind of takes my mind away from everything that's going on.
CARRY SANDERS: Today, Lutheran church charities deployed the Comfort Brigade at Tufts Medical Center; dogs that have recently been working with other recovering children in Newtown, Connecticut. Quiet, peaceful visitors, who Leighanne Yanny says, set her nerves at ease just hours before the surgery on her wounded leg.
LEIGHANNE: Animals, you know, they just have a different sense. You know, they don't-- they don't talk back to you.
WOMAN: Oh my goodness. Hi.
CARRY SANDERS: The comfort dogs are like furry therapists, and it's not just those who were injured that need relief.
How nice is it for you to have just a different moment here with a dog?
WOMAN 2: My stress level has gone way down.
CARRY SANDERS: They sense love.
TIM HETNER: They sense that somebody is caring. And they sense that, in the midst of darkness, there's light.
This is Luther.
CARRY SANDERS: Companionship, compassion, and comfort when it's needed the most.
LEIGHANNE: You are a big puppy for two.
CARRY SANDERS: Carry Sanders. NBC News, Boston.