An Improv Everywhere prank at a Manhattan Gap store earlier this month featured some unexpected players after a manager called police to report a flash mob.

Participants entered the store's Fifth Avenue location wearing white Morphsuits underneath Gap-style clothing to imitate mannequins. All 40 people were instructed to zip up the suits at a pre-determined time, and pose next to real mannequins for about five to 10 minutes before leaving the shop. Gap patrons and employees appeared to be amused by the hijinks, but before the prank was completed, the police arrived and began handcuffing participants.

"We were very surprised at the response," Improv Everywhere founder Charlie Todd told Mashable. "It was distressing to see these people who were just helping me out down on the floor in handcuffs."

Some participants saw what was happening, and managed to leave the store unnoticed after unzipping their suits. However, 20 people, including Todd — who did not pose as a mannequin, but identified himself as the organizer — ended up handcuffed on the store's tiled floor.

Image: Arin Sang-urai

Todd said he believes police assumed the prank was a robbery, thanks to recent group heists in multiple cities, including Washington, D.C. and Chicago, which have been dubbed "flash-mob robberies." However, once participants were allowed to unzip their Morphsuits, revealing a wildly diverse group of people that included 20-somethings and senior citizens, it was obvious that the police's theory was unfounded, Todd said.

After they realized no crime had occurred, officers uncuffed the participants, and let them go. As it turned out, one cop had even participated in another Improv Everwhere prank, the MP3 Experiment, last summer at New York's South Street Seaport.

No charges were filed against any of the participants. The store's manager considered banning them from Gap for life, but eventually decided not to take action, according to a post on the Improv Everywhere website. Gap confirmed to Mashable that no one was banned for life, and that participants were just asked to leave the store.

"The safety of our store associates and customers is always our main concern," a Gap spokesperson told Mashable. "When a recent in-store flash mob upset our customers, our team members followed protocol to restore order. We are pleased to report that no customers, employees or mannequins were injured in this event."

Despite the confusion, participants were still positive about their experience.

"I'm so glad I did it, it was fun, it's going to make for a great story," one participant said in a video, above, documenting the prank.

Improv everywhere has done about 20 pranks in retail stores, including Staples, Macy's and Starbucks, all of which were completed without much hubbub. The last time police were called in was during a prank at Best Buy eight years ago when participants posed as fake employees.

"I learn a little bit from every project I do," Todd said. "I probably won't do this exact project any time soon, but I don't like to repeat myself anyway. I'm not mad at the Gap, and I hope they're not too mad at us."