[T, I] ~ (sth)if a person or an animal flares their nostrils(= the openings at the end of the nose), or if their nostrils flare, they become wider, especially as a sign of anger （尤指因气愤）使（鼻孔）张开，（鼻孔）张开
The horse backed away, its nostrils flaring with fear.
马向后惊退，吓得鼻翼扇动。