Plain air-popped only — skip the butter and salt.
A few pieces of plain air-popped popcorn are harmless. Butter, salt, and flavorings make it a junk food, and unpopped kernels are a choking hazard. When in doubt, skip it.
Proceed carefully and follow the guidance above. When in doubt, skip it — there are plenty of unambiguously safe treats to choose from.
Get the printable list of the 30 most dangerous foods for dogs.