theres no such thing as a "teacup" > http://www.cnmchihuahuas.com/teacup.html most people think they are getting a teacup animal when really its just a normal sized one but its a puppy and it will eventually grow to normal size
that question would be hard to answer but my chihuahua is pretty smart and since they have big heads they can hold big brains so i am guessing they have big brains
Chihuahua breeders often use terms like miniature, teacup, tiny toy, apple headed, or deer headed, to describe puppies. These terms are not recognized by the breed standards and may be misleading....