A man sees an advert for jobs at the zoo - "no experience necessary - just turn up on Tuesday and ask for the manager" - so he goes along and finds out more. The manager tells him that their monkey breeding plan hasn't been as successful as hoped, so they need a few people to dress up in monkey suits, make monkey noises and swing around on tree branches. The man thinks it sounds easy, so he gets the job and does it for the next three weeks.
Being a human, he doesn't have the same natural tree-swinging skills as an actual monkey, but he persists and improves a lot, to the extent that he's a real hit with the visitors, who stand and watch him for ages.
One bank holiday, the space outside the monkey enclosure is absolutely packed, with hundreds of people watching the monkeys intently - and this 'monkey' and his skills in particular. He decides to give them a great show and goes for a huge swing on a high up branch and swings around it three times... until he loses his grip and goes flying over into the lion enclosure right next door.
A huge, fierce lion with a glorious mane and a look of pure strength, power and determination in his eyes spots him and heads towards him, running faster and faster. The poor man is absolutely petrified and is rapidly soiling his monkey suit. He howls louder and louder, with all the onlookers watching on rapt to see nature in all of its brutal reality. He can no longer keep up the loud monkey-like howls, so he starts screaming out "Help me! Help me! I'm not a monkey, I'm just a man in a costume! Save me, somebody, please!!"
All of a sudden, the lion darts forward and is inches away from him. As he sobs, trembles and gulps, preparing to face his final destiny, the lion says in a loud whisper "Shut up, you absolute muppet; just shut up, SHUT UP!!! Do you want to get us both fired?!?!"