09-27-2017, 07:24 AM
Both open. Closing one nostril increases the chance of busting a blood vessell in your nostril which could cause a nose bleed that can last for days if not cauterized. Been there done that. However, most articles will advise to close one nostril and blow GENTLY. I guess Gently is not something I see as a nasal canal cleaner. So technically, you are correct according to the internets. Dr. Dog.