Can a Chihuahua eat popcorn?
Plain, yes, with no salt or butter.
How much: 3-4 pieces of plain popcorn at most, with nothing added.
Why
Plain popcorn is just puffed corn and harmless. The problem is the salt, butter and oil added to it. Unpopped kernels are a choking hazard.
Popcorn in a Chihuahua's diet
Keep in mind how tiny the portions are for this breed: an adult Chihuahua eats roughly 1 to 2.3 ounces (25-65 g) of food a day depending on his weight, and treats shouldn't go over 10% of his daily calories. That's only a small fraction of an ounce. What looks like "a little bite" to us can be half a meal for him.
This information is for general guidance and is not a substitute for advice from a licensed veterinarian. Every Chihuahua can react differently; if in doubt, always check with a professional.