For the size comparison I just estimated: a mammal&#x27;s avg density isn&#x27;t much more than 1 and the volume of a chihuahua is about the size of my Wolfhound&#x27;s brain case (I see both kinds of dog daily).<p>The &quot;intelligence&quot; point is both uncontroversial and well attested: consider, for example, that you can train any dog to an agility course (adapting for size constraints of course) and in dog shows this is very common.<p>There are certain breeds of dog (or horse) that are considered &quot;more intelligent&quot; than others, but this rarely holds up under scrutiny -- some are more gregarious than others but all are apparently equally trainable to the kinds of tasks humans typically ask.  Some are more gregarious than others or have other traits but they are well within the variations humans also exhibit.<p>HTH