Your chihuahua mix is food aggressive. That's bad. When he or she growls when food is present, pick up the food for a few minutes when behavior stops give the food back, when he or she growls when food is present remove the food again, be consistent with this behavior until he/she realizes that growling takes the food away. If there is no growling when food is present reward with praise and petting. A dog's attention span is about 15 minutes discipline should never last longer than that For food aggression training 2 to 5 minutes per episode should be sufficient depending on the severity of each individual episode. Five minutes is for the most severe. Also, let the dog know you are the big dog, you can demonstrate this by covering the food bowl with your body and holding the food between your feet, which says "this is mine", you can allow your dog to eat while you maintain possession of the food with your body position. And before you allow your dog to eat, he must think you are eating first because you are the alpha dog and your pet must understand he/she is the beta dog and may only eat after you have finished, so pretend to eat some of the food in front of your dog before the bowl is offered to him/her. Be consistent and patient. This will take a little time. Plan on being there with your dog at meal times. When you are away during his/her feeding time always check to make sure he/she has eaten. Sometimes a dog will stop eating unless you are present. If he/she has not eaten feed him/her. Persistence Pays.