He said the pranking occurred during cooling down time for the actors while filming this week's fiery episode, which saw Naufahu's character Khal Moro killed by Clarke's Daenerys when she sealed him inside a blazing tent.
It wasn't the only time he was pranked. Naufahu also said Clarke would also write Dothraki words on his body while he slept.
"A lot of it was, 'Qoy Qoyi,' which means 'blood of my blood' ... maybe she was delirious from all the propane on set," he said.
Read more: How Kiwi actor Joe Naufahu found himself terrorising Daenerys on Game of Thrones
But in an interview with the Herald, he said he got his own back, sneaking Tongan and Samoan words into Dothraki - a made-up language used on the show - during rehearsals.
"It sounded quite similar to Samoan and Tongan so I'd slip words in and they'd never know. I was a bit scared to do it in the takes, but I'd add a Samoan word or Tongan word here or there into rehearsals. Emilia caught wind of it and she started throwing her own made up words in there to throw me," he said.
