The main difference between these two dogs is that Chi puppies are generally less active than Cairn dogs. The latter is known for its playful and high-energy character, which is not the case with their Central American counterparts. Cairn Terriers are prey-oriented as they have been hunting dogs for a very long time. On the other hand, Chi puppies are lap dogs by default, and they enjoy a calmer lifestyle. Still, there are many common traits that these two breeds share. For instance, both of these canines can be aggressive at times, especially Chihuahuas. Why Chi dogs are so aggressive has to do with their natural self-defensive mechanism.