Ace and I spend a lot of time joking about what we think the dog thinks.
"He thinks we're crazy." "He wants food." "Leave me alone already people!" "You've got food, you might give it to me, therefore I must stare at you." "Food! Food! FOOD! FOOD!" "I'm going for a ride! Oh, wait, they're leaving me here."
Of course, we still can't figure him out when there is a vehicle that is open and you say in (pointing to the house) and he jumps in the car. He apparently feels the need for rides more often than he gets them.
But mostly, I think he just thinks "I'm hungry!", "Fetch?", or "Can I go for a ride? Can I? Can I?" and usually, it's not a good time for that.