Do all chihuahuas' ears stand up?

Purebred Chihuahuas have round skulls with erect ears that appear more erect when the dog is at attention. The ears may appear to flatten when the Chihuahua is relaxed, but the dog is bred to have ears that stand up straight.

One illness Chihuahuas are susceptible to is molera. This is a condition where there is a hole in the skull, which can affect the appearance of the head. Veterinary care is needed for Chihuahuas that have molera.

Chihuahuas don't breed all the same size. One litter can have Chihuahuas that vary in size as adults. Chihuahuas are known to shiver or shake when cold or stressed out.