What happens next?

How to feed picky chihuahuas
Take a trip to the vet.
If your chihuahua is a normal, regular eater and stops eating within a short period of time, i.e., a week, this can indicate a problem. Inappetence is a symptom of many dog illnesses.
If this is your dog, then you need to take it to the vet immediately, especially if it is coupled with weight loss, and/or vomiting and diarrhea. Hormonal changes, such as females in heat, could also be a reason for why your dog is eating less.