It looks like Thog was performed the same way as Big Bird, with the performer using his right arm to work the head (and possible controll the eye movement) and his left arm to operate the left arm. i am not sure if the performer could switch his right arm from the head to the right arm. There was probably a monitor inside thog, and there was also probably a mechanic inside the character that could make the ears go up. I guess Thig was performed in a similar way.