More than 150 staff members were seen chasing keeper Natsumi Uno around Ueno Zoo, as she tried to mimic what a real-life gorilla would do if it broke free.
Despite the unrealistic gorilla suit, the staff - including cops and firemen - took the drill very seriously. They pointed stun guns at Natsumi and prodded her with sticks before trapping her in a net.
Natsumi seemed very happy to have volunteered to become an ape for the day.
She said: "We never normally get the chance to get caught."
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