The case of mistaken identity took place at the Loro Parque zoo in the Canary island of Tenerife on Wednesday.
As part of a drill to find out how to deal with the potential escape of one of the park’s apes, one of the workers dressed up in a gorilla costume to make the whole scenario all the more believable.
Unfortunately for him, one of the vets must have not been informed about what was happening.
When he saw a furry 'beast' outside its cage, he quickly grabbed his rifle and shot it, or him, with a narcotic dose meant for a 200-kilo mammal.
The man not only fell to the ground like a ton of bricks, he also suffered an allergic reaction which made his condition all the more serious, La Opinión de Tenerife reported.
When emergency services arrived at the scene, they found him lying unconscious in his underpants.
On Friday, a Loro Parque spokesperson denied the man was in a gorilla suit and said the tranquilizer rifle had simply misfired .
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His condition is now stable and local authorities are investigating how the unfortunate event happened, given that there was a risk assessment team present at the zoo when the drill took place.