Cedric and Bertrand want to see a movie. Bertrand wants to see Muscled Duded Blow Stuff Up. Cedric wants to see Quiet Remembrances: Time as Allegory. There's also Middlebrow Space Fantasy. They are rational but not selfish - they care about the other's happiness as much as their own. What should they see?
Right - it's a little misleading to cast the decision procedure as if it was some person-independent thing. If you make a decision based on how happy you think the puppy will be, it's not because some universal law forced you to against your will, it's because you care how happy the puppy will be.
If there's some game-theory thing going on where you cooperate with puppies in exchange for them cooperating back (much like how Bertrand and Cedric are cooperating with each other), that's another reason to care about the puppy's preferences, but I don't think actual puppies are that sophisticated.