This is Terryn wearing his vampire teeth. He can put them in himself... although he seems to have trouble with it in the video. Usually he puts them in and growls like a monster. In this video... he mostly just drools a lot and smiles.
One of Terryn's favorite movies is Monsters VS Aliens. There is a part where one of the characters does a DDR-like scene to save the planet. Terryn always gets up and dances to the part. Here he is demonstrating.