Emily Deschanel and David Boreanaz

The Bones producers freely admit that when they conceived Monday's episode, they had no idea it would wind up being the Fox drama's milestone 150th episode. But they're pleased with the happy accident.

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The episode, "The Ghost in the Machine," was originally written and shot last season as one of four "bonus" episodes the show produced when they were given a shortened season because of Emily Deschanel's pregnancy.

"We had to shoot four episodes that didn't fit into the timeline of the Bones timeline, and at first we were very, very cranky about that," creator and executive producer Hart Hanson tells TVGuide.com. "Then we realized it gave us an advantage in that we could do stuff we hadn't done before. I've always wanted to write this crazy episode where the skull is the camera, and we see everything from the victim's point of view. It's not the kind of thing you would generally do in a run-of-the-mill Bones episode, and this gave us the chance to do it. It was a big risk and I think it turned out [well]."

Because the episode is such a departure for the show, it fits naturally as a milestone episode. Plus: It features the return of Cyndi Lauper's Avalon Harmonia, who senses that the teenage victim's spirit is still present in the remains. Although Dr. Brennan (Deschanel) remains skeptical about the existence of a human soul from a scientific standpoint, viewers will get an up-close look at how the rest of the Jeffersonian team feels.

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"We see intimately how each character tends to interact with a victim when no one else is around — the things they say, what do they do," Hanson says. "[There is] the oddness of watching a scripted television show and having the actor look into your eyes when they are acting. It's a real connection."

Those personal moments also help reveal the true emotional weight of the case. "We found out in the first season of Bones that if the victim is a child, you cannot be funny," Hanson says. "This is not a funny episode. It's not one of our laugh riots. There's a few giggles but it tends to be a bit more serious."

But executive producer Stephen Nathan says the weighty material also provides a welcome opportunity to further explore Dr. Brennan. "It gave us an opportunity to see Brennan personalize a victim," Nathan says. "She was kind of trying on for size this notion that there might be a spirit in there. She didn't believe there was a spirit in there, but in spite of herself, got caught up emotionally and that's always nice to see in Brennan. We're seeing it more and more because she's evolving, but it's still a rare event."

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It's that evolution that's been key to the show's longevity — and the producers say it will remain key as they head toward the next 150 episodes. "She had a baby, and a baby touches your soul whether you think you have a soul or not," Hanson says of his heroine. "There's a little tiny crack in her heart because of this baby and Booth [David Boreanaz], and that makes her open to more things and more open to the world her child lives in."

Adds Nathan: "In [Season 8], there's certainly the evolution of Brennan. If Brennan was the same way she was in Season 1 or Season 2, people would not still be watching this show."

Bones airs Mondays at 8/7c on Fox.