"Bones in your corset," she said, to the agreement of showrunner I. Marlene King.
In Season 4, Spencer and the other girls participated in a bridal charity show, which resulted in Spencer being chased through the woods and ultimately finding Ali's supposed bones lining her wedding gown.
"It was more the worst because she'd run all over woods, she tripped, she was bleeding, she almost got snapped in a bear trap," Bellisario recalled. "I had to do it all in a corset and I couldn't breathe ... And at the end of it, she pulled [the dress] off] and it was human bones."
Watch Bellisario recount the full story in the video above.