Seoul, South Korea (CNN) -- Korean is considered one of the hardest languages in the world to master, but an elephant in a South Korean zoo is making a good start. 

Koshik, a 22-year-old Asian elephant has stunned experts and his keepers at Everland Zoo near Seoul by imitating human speech. Koshik can say the Korean words for "hello," "sit down," "no," "lie down" and "good." His trainer, Kim Jong Gap, first started to realize Koshik was mimicking him several years ago. 

""In 2004 and 2005, Kim didn't even know that the human voice he heard at the zoo was actually from Koshik," zoo spokesman In Kim In Cherl said. "But in 2006, he started to realize that Koshik had been imitating his voice and mentioned it to his boss." 

Why do elephants have hair on their heads? 

His boss initially called him "crazy." 

Koshik's remarkable antics grabbed the interest of an elephant vocalization expert thousands of kilometers away at the University of Vienna in Austria. 

""There was a YouTube video about Koshik vocalizing, and I was not sure if it was a fake, or if it was real," Dr. Angela Stoeger-Horwath said. She traveled with fellow expert Dr. Daniel Mietchen to South Korea in 2010 to test the elephant's ability. They recorded Koshik repeating certain words his keeper said and then played them for native Korean speakers to see, if they were recognizable. 

"It is, for some of the sounds he makes, quite astonishing for how similar they are," said Mietchen of the University of Jena in Germany. "For instance the word 'choa' (meaning good) -- if you hear it right after what the keeper says -- it's quite similar." 
What is one of the hardest languages to master?
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Korean
Korean is considered one of the hardest languages in the world to master
an elephant
an elephant in a South Korean zoo is making a good start. 

in a  zoo
an elephant in a South Korean zoo
Everland Zoo
at Everland Zoo near Seou
Seoul
Everland Zoo near Seoul
Koshik
Koshik, a 22-year-old Asian elephant
22
Koshik, a 22-year-old Asian elephant
unknown
unknown
Dr. Angela Stoeger-Horwath
There was a YouTube video about Koshik vocalizing, and I was not sure if it was a fake, or if it was real," Dr. Angela Stoeger-Horwath
an elephant vocalization expert
grabbed the interest of an elephant vocalization expert thousands of kilometers away at the University of Vienna in Austria. 

at the University of Vienna
 an elephant vocalization expert thousands of kilometers away at the University of Vienna in Austria
traveled  to South Korea
She traveled with fellow expert Dr. Daniel Mietchen to South Korea
no
She traveled with fellow expert Dr. Daniel Mietchen
Dr. Daniel Mietchen
She traveled with fellow expert Dr. Daniel Mietchen
2010
traveled with fellow expert Dr. Daniel Mietchen to South Korea in 2010 
recorded Koshik
They recorded Koshik repeating certain words his keeper said
no
"It is, for some of the sounds he makes, quite astonishing for how similar they are," 
mimicking the trainer
 Koshik was mimicking him several years ago
Kim Jong Gap
His trainer, Kim Jong Gap
on YouTube
There was a YouTube video 