By LAUREN EFFRON and VICTORIA THOMPSON

When actress Troian Bellisario, who plays Spencer Hastings on "Pretty Little Liars," started noticing meditation imagery in her character's bedroom, even she didn't know it was placed there for a reason.

"They started putting up this really great imagery of, sort of like, meditation and Buddhism, and I really didn't know where that came from," Bellisario told "Nightline." "And then they told me that they thought that I picked up meditation when [my character] was hospitalized, and I was like, 'that would have been cool to know.'"

Fans of the smash hit ABC Family show might recall those Season 3 episodes when Spencer was institutionalized after finding out her boyfriend Toby, who is played by Keegan Allen, was a member of the "A" team, which torments her and her friends. After Spencer was released from the hospital, that's when Bellisario said she noticed set designers started adding new Zen pieces to Spencer's bedroom.

"I have all this cool art, like these Zen garden things and meditation bells. This is all new," she said. "I'm into it."

Bellisario took "Nightline" on a tour of Spencer's bedroom as part of a larger piece about decoding one of the most popular shows on television - it's the most tweeted about show in history.

She pointed out several elements of the bedroom that help define her character, and explained why even the photos in the room are special.

"The cool thing is in all of the girls' rooms… we have actual pictures of us when we were little," Bellisario said. "These are actual pictures of me growing up. You can see I'm a little munchkin."

Watch the full story about the "Pretty Little Liars" cast on "Nightline" TONIGHT at 12:35 a.m. ET.