Tiny pet with a super-sized brain

The chihuahua hails from the Mexican state of the same name

They are the world’s smallest breed of toy dog, weighing in at anything from 2lb to 6lb – barely a third of the average cat

Newborn puppies can fit in the palm of a human hand; litters usually number four

The dogs have such fragile necks that owners are advised to use harnesses rather than leads to protect them from injury

Relative to their bodies, chihuahuas have the biggest brains in the canine world

They were worshipped by the Aztecs and highly prized because of their size and intelligence

Like human babies, chihuahuas have a soft spot on their heads, which may last for life