Chihuahuas have the biggest brain relative to their bodies in the dog world

Don't worry, Chihuahuas don't have oversized brains similar to those of the aliens from Mars Attacks. They really win this on the basis of the rest of their bodies simply being so tiny. Chihuahuas are quick witted and actually easy to train comparative to other dogs but if you think that makes them easy to housbreak you may want to rethink your adoption decision. Their headstrong personality and small bladder make them very difficult to housebreak.