The Brit portrays dragon queen Daenerys Targaryen on the show and regularly slips into the fictional language.
She tested castmates and crew in one recent scene by showing off her linguistic skills.
"It was the end of the day... and we were goofing around...," she told U.S. chat show host Seth Meyers, "so I thought it would be funny if I did MmmBop in Dothraki."
And she thinks some of what she said may have made it onto the programme, because no one on set really knows what she's saying.
"They don't know," she added. "Everyone's like, 'Can we go back to the bit, where... Just go from the top'."