Syntax

Syntactic actants

Actant 1: whose nostrils they are
(a) Genitive
(b) Possessive
Ноздри Тани гневно вздрагивали. Tanya's nostrils quivered angrily.
Ноздри его гневно вздрагивали. His nostrils quivered angrily.
NB When the word ноздри functions as a subject and does not have a descriptive modifier, the construction ноздри у + Genitive is often preferred to (a) and (b), above:
Ноздри у мальчика были заткнуты ватой. The boy had wads of cotton in his nostrils.

Restrictive modifiers

(a) adjectival modifier
левая/правая ноздря the left/right nostril
Левая ноздря у мальчика была заткнута ватой. There was a wad of cotton in the boy's left nostril.