He who smells it
If you’ve ever owned a dog, you’re probably familiar with their habit of farting in their sleep. Everything they do is so sweet and innocent, we can’t be mad at them, even if they stink up the room. They mean no harm. This good boy startled himself awake, and you can see in the apologetic look on his face a mixture of fear and shame.
Besides, it seems like he’s already suffered enough from this fart, why give him a hard time about it? It’s only natural, and unlike us humans, dogs have no control over it, and they don’t know it’s considered impolite (incidentally, they aren’t familiar with the concept of manners).