We're unsure if this dog belongs to anyone on stage, or if it's just a passerby, but it obviously appreciates fine music. It happened to the Vienna Chamber Orchestra, and everyone took it in stride perfectly. None of the musicians stopped, the crowd gave an appropriate roar, and the dog, well the dog was a good dog and laid down to enjoy the music. 

http://streamable.com/heskt

I'd have to imagine everyone in attendance had a better time because of it. Good work doggo.