He is, for the moment, completely dead to the world, as long as Al keeps hitting that part of his hide. It's impossible for him to reach and very, very difficult to rub against something, and always becomes very itchy due to the way the scales interact. As a result, when it's scratched by a viking, it turns dragons into pudding. Most dragons, at least.

Toothless' tongue lols out of his mouth as he lets out a slightly higher whine. Don't stop, please, Al!