if a person or an animal flares their nostrils(= the openings at the end of the nose), or if their nostrilsflare, they become wider, especially as a sign of anger
گشاد شدن سوراخهای بینی, پهن شدن سوراخهای بینی, باز شدن سوراخهای بینی
The horse backed away, its nostrils flaring with fear.