The actress stars in the American teen drama series, which is loosely based on the book franchise of the same name by Sara Shepard and follows a group of girlfriends who drift apart after one of their pals goes missing.

Now in its seventh season, Shay and her fellow castmates, including Lucy Hale, Ashley Benson and Troian Bellisario, have all been sworn to secrecy to keep plot details secret from fans. But the Canadian-born beauty reveals she once accidentally left one of her scripts, which was watermarked with her name, in a very public place.

"So when we have these scripts for table reads they have our names on them, and if we lose them you're in big trouble," she said during an appearance on The Tonight Show with Jimmy Fallon on Monday night (25Jul16). "Well, I left mine one time in a Whole Foods... I was driving in Santa Monica and I was like 'Oh my gosh, I can't believe I left it.'"

Accordingly, the 29-year-old bolted back to the store but was dismayed to find an "older woman" sitting at a booth reading it. Shay said she tried to explain that the script belonged to her, but the woman was hesitant to hand it over, leading to the pair trying to grab it off each other.

"She's like, 'Well, this says S. Mitchell, are you S. Mitchell?' And now I'm playing tug of war with this older woman in Whole Foods, trying not to cause a scene!" she laughed to host Jimmy.

While Shay didn't divulge any details about what twists viewers can expect in upcoming episodes of her popular show, she did reveal that she herself has been caught out for lying before. As a teenager, Shay used a friend's ID card to get into a nightclub, but the experience turned out to be a short-lived one.

"I got into a club and all of a sudden I feel this tap on my shoulder and I turn around and it's my dad and he's like, 'Can I have this last dance?' and I was like 'Oh my gosh!'" she shared, adding, "It was kind of awkward!"