Beautiful actress Choi Ji Woo went through a mental breakdown on the latest episode of 'Running Man'.

As she first arrived on the set, she was greeted by a familiar mission card: the position of the coveted 'spy'. Excited at her prospects of winning, she began to make plans for her eventual domination over the 'Running Man' members.

Unfortunately, she was unaware of one critical fact: the entire cast was listening in to her conversation via a video monitor! The entire episode, in fact, was based around tricking Choi Ji Woo to believe that she was, indeed, the spy - until the very end.

After the final mission was over and Choi Ji Woo believed herself to have succeeded, the rest of the cast members clued her in on the big secret, upon which she broke down, yelling, "Wait. Why does 'Running Man' like to deceive everyone?"

"I didn't think anything was wrong," she said ruefully, after she had recovered from the shock. "I really thought I was fast and my footsteps were as light as a feather."

Any Running Man would be able to tell you that tricks and deceit are all a part of 'Running Man', Ji Woo - maybe next time!

Check out the full episode below!